VALLEY RESEARCH

Research News is a digest of science and technology news items arising from research and development magazines, newspapers, trade magazines, newsletters, and other news sources that Valley Research processes daily for the benefit of its customers everywhere. It is provided freely to our customers who are free in turn to post or transmit it to other interested researchers provided only that credit to Valley Research is given. Research News is updated approximately once a week.

Rodolfo Carrera, Editor

WEEK OF FEBRUARY 17, 2025 [No. 1615]

Nuclear-spin dark state observed:   researchers at University of Rochester in Rochester, NY have used dynamic nuclear polarization to align atomic nuclei spins in a gate-defined Si double quantum dot to provide direct evidence of the nuclear-spin dark state where nuclei synchronize reducing their coupling with electron's spins, thus decoupling nuclei and stabilizing electron spins. They show that the transverse electron–nuclear coupling rapidly diminishes in the dark state, and that this state depends on the synchronized precession of the nuclear spins. The dark state significantly reduces the relaxation rate between the singlet and triplet electronic spin states.

For more information: Phys.org, February 12 (2025); Nat. Phys., January 28 (2025).

Topological chiral superconductivity:   researchers at the MIT in Cambridge, MA have proposed conditions under which superconductivity can arise from the electrons’ own mutual electrostatic repulsion in a 2D lattice. They predicted different superconducting states, all chiral. Some of the states have quartet charge condensations. The electron's dispersion ~ k⁴ (rather than having the usual k² energy dependence). As in regular superconductivity their energies must be lower than that of their cooled parent state. That parent state is one of two exotic electronic states characterized by strong repulsive interactions (not clear yet which one). The resulting superconductors break both time-reversal and reflection symmetries in the orbital motion of electrons, and they exhibit nontrivial topological order. Their findings suggest that this topological chiral superconductivity is more likely to emerge near or between a fully spin-valley polarized metallic phase and a Wigner crystal phase. These topological chiral superconductors can be fully or partially spin-valley polarized. For partial spin-valley polarization, the ratios of electron densities associated with different spin-valley quantum numbers are quantized as simple rational numbers. Many of these topological chiral superconductors exhibit charge-4 or higher condensation, neutral quasiparticles with fractional statistics, and/or gapless chiral edge states. Two of the topological chiral superconductors are in the same phases as the “spin”-triplet or spinless p + ip BCS superconductor, while others are in different phases than from any BCS superconductors.

For more information: Physics, February 11 (2025); Phys. Rev. B, January 10 (2025) page 014508.

WEEK OF FEBRUARY 10, 2025 [No. 1614]

1D phase change observed:   researchers at the University of Maryland in College Park, MD and Duke University in Durham, NC have observed a finite-energy phase transition in a 1D ion array quantum simulator. They show that finite-energy states can be generated by time-evolving prepared initial states and letting them thermalize under the dynamics of a many-body Hamiltonian. By preparing initial states with different energies, they study the finite-energy phase diagram of a long-range interacting quantum system. They observe a ferromagnetic equilibrium phase transition as well as a crossover from a low-energy polarized paramagnet to a high-energy unpolarized paramagnet, in agreement with numerical simulations. The researchers use Au electrodes to create electromagnetic fields that trap dozens of ions in a chain geometry just above the surface of the electrodes. They use laser beams to induce interactions between the ions, thus, establishing a long-range interaction 1D magnet. The researchers simulated a system of 23 ⁷⁰Yb ions arranged into a 1D chain. The difficulty on effectively heat the system and observe a phase transition as a function of energy lies in coupling to a heat bath without disrupting the quantum state. To solve the problem of realizing interactions over sufficiently long distances and preparing equilibrium states, the researchers prepared the ions in a heated initial condition and then allowed them to evolve following their own dynamics via long range interactions. This evolution mimicked the effects that would follow an increase in temperature. Using this method, they observed the system transition from a ordered magnetized state to a disordered unmagnetized state, confirming the occurrence of the phase change.

For more information: Phys,org, February 6 (2025); Nat. Phys., January 17 (2025).

Ambient pressure HTS superconductivity in bilayer nickelate demonstrated:   researchers at SLAC in Menlo Park, CA have demonstrated that lateral compression from substrates can stabilize a superconducting state in thin film La₃Ni₂O₇ at room pressure. They present signatures of superconductivity in La₃Ni₂O₇ thin films at ambient pressure, facilitated by the application of epitaxial compressive strain. The onset T_c varies approximately from 26 K to 42 K, with higher T_c values correlating with smaller in-plane lattice constants. They observed the co-existence of other Ruddlesden-Popper phases within the films and dependence of transport behavior with ozone annealing, suggesting that the observed low zero resistance T_c ≈ 2 K can be attributed to stacking defects, grain boundaries, and O stoichiometry. The nickelate studied here has been shown to have Tc ≈ 80 K at high pressure. The researchers observed that the sample's T_c ≈ 26 K to 42 K depending on the level of compressive strain. While the material enters the superconducting phase at these temperatures, defects in the nickelate and the O atom ratio produce T_c ≈ 2 K. They have demonstrated that lateral compression from substrates can stabilize the material, even though it differs from the uniform compression achieved through squeezing it evenly from all directions, similar to that produced by a diamond anvil cell. The researchers plan to refine the material's crystalline quality and explore doping strategies.

For more information: Phys.org, February 5 (2025); Nature, December 19 (2024) page 935.

WEEK OF FEBRUARY 3, 2025 [No. 1613]

Chirality-induced directional spin selection observed:   researchers at the Johannes Gutenberg -Universität Mainz in Maiz have studied the chirality effect on spin in hybrid metal/chiral molecule thin-film heterostructures. Their observation of spin-dependent transmission of electrons through chiral molecules has confirmed the existence of the chiral-induced spin selectivity (CISS) effect with chiral-induced unidirectional spin-to-charge conversion. They inject a pure spin current via spin pumping and investigate the spin-to-charge conversion at the hybrid chiral interface, observing chiral-induced unidirectionality in the conversion. Angle-dependent measurements reveal that the spin selectivity is maximum when the spin angular momentum is aligned with the molecular chiral axis. They did not pass the charge current directly through the chiral molecules themselves. Instead, they created a hybrid system that consisted of a thin film of Au with chiral molecules on it. Although the major part of the current flows through the Au film, the presence of the chiral molecules alters the state of the Au component. They were interested in how the spin current was converted to a charge current. In a film consisting of pure Au, ~ 3% of the spin current is converted to charge, regardless of electron spin orientation. In the hybridized system of the Au layer with chiral molecules if the molecules on the surface of the Au are right-handed, currents with electron spin-up are converted much more efficiently to charge than those with spin-down. The outcome is the opposite if molecules on the Au surface are left-handed. This effect occurs only if the spin is in the same or opposite direction to the helix structure of a chiral molecule. If the direction of spin is not aligned with the direction in which the helix structure is arranged, the effect does not occur. The researchers demonstrate the impact of chiral molecules on the inverse spin Hall effect (ISHE), which originates from a collection of relativistic spin-orbit-coupling (SOC) phenomena. For this, they inject a pure spin current generated by ferromagnetic resonance in a ferromagnetic insulator into a hybrid metal/chiral molecule bilayer. The SOC of the hybrid layer converts the spin current into an electromotive force via the ISHE, measurable as a voltage signal across the metal layer. The results show a chirality and spin polarization–dependent unidirectional ISHE in the hybrid chiral system confirming that SOC plays a key role in this CISS effect.

For more information: Phys.org, January 30 (2025); Science Advances, January 1 (2025).

Weakly-driven spin squeezing entanglement in atomic arrays:   researchers at JILA in Boulder, CO have investigated the driven-dissipative dynamics of multilevel atomic arrays interacting via dipolar interactions at subwavelength spacings. They find that unlike two-level atoms in the weakly excited regime, multilevel atoms can become strongly entangled. The entanglement manifests as the growth of ground state spin waves persisting after turning off the drive. They propose the 2.9  μm transition between ³P₂↔︎³D₃ in ⁸⁸Sr with 389 nm trapping light as a platform to test their predictions. In dipole-dipole atom interactions in a lattice, the state of the system can become correlated. In the absence of an external drive, the generated entanglement typically disappears since all atoms relax to the ground state. If atoms have more than two levels participating in the process, then system interactions and complexity drastically increase. The researchers here have studied atom-light interactions in the case of effective four-level Sr atoms, two metastable ground and two excited levels arranged in specific 1D and 2D crystal lattices, with atoms closer to each other than the wavelength of the laser light used to excite them. The study concentrated on a set of internal levels with a much smaller energy separation than typical optical transitions. Instead of using truly ground-state levels, they proposed using long-lived metastable levels. By creating a long-lived metastable excited state, a 2.9-µm wavelength transition between this state ³P₂ and another excited-state ³D₃ state.(about eight times longer than the usual separation between nearby atoms trapped in an optical lattice) is accessed here. By having a transition wavelength much longer than the trapping light wavelength, they can realize strong and programmable interactions via the photon exchange that happens when the atoms are set close to each other. The atoms need to be very close, as interactions weaken with distance, eventually becoming lost due to other sources of decoherence. Keeping atoms close allows interactions to dominate, preserving the growth of entanglement. They work in the weak and far-from-resonance regime where atoms are allowed to virtually exchange photons, moving them between ground states without permanently occupying an excited state. In the metastable state dynamics, they observe growing correlations, which can be preserved when the laser is turned off. In this regime where the excited levels are only virtually populated, and only atoms can occupy the metastable state levels, the four-level problem can be reduced back to a two-level system although dealing with much more complex interactions including multi-atom interaction. Considering the far-from-resonance regime (in leading order, only two atoms interact at a given time), the Hamiltonian describing the metastable state dynamics maps back to a know spin model. Thus, they studied spin waves across the lattice arrangement. By controlling the polarization and propagation direction of the photons of the laser exciting the atoms, the researchers could determine which spin-wave pattern became dominantly entangled. The entanglement observed was spin-squeezing with increased sensitivity to external noise. The spin squeezing in the system can be experimentally measured and serves as a witness of quantum entanglement. This finding implies that quantum systems could maintain entanglement over long periods, without needing constant intervention to prevent decoherence. One key limitation here is dipole-dipole interactions, which involve long-range forces that couple atoms both near and far in the lattice. These couplings are anisotropic and depend on the relative orientation of the atomic dipoles, making the system more complex. Each atom interacts differently with its neighbors spaced along different directions in the lattice, leading to varying interaction strengths and signs across the array.

For more information: Phys.org, January 27 (2025); Phys. Rev. Lett., December 3 (2024) page 233003.

WEEK OF JANUARY 27, 2025 [No. 1612]

Rydberg state thermometry with mm blackbody emissions demonstrated:   researchers at NIST in Boulder, CO have performed primary quantum thermometry of mm-wave blackbody radiation (BBR) via induced state transfer in Rydberg states of cold atoms. Rydberg states of alkali-metal atoms are highly sensitive to electromagnetic radiation in the GHz-to-THz regime because their transitions have large electric dipole moments. The researchers track the BBR-induced transfer of a prepared Rydberg state to its neighbors and use the evolution of these state populations to characterize the BBR field at the relevant wavelengths, primarily at 130 GHz. They use selective field ionization readout of Rydberg states and substantiate their ionization signal with a theoretical model. Using this detection method, they measure the associated BBR-induced time dynamics of these states, reproduce the results with a simple semiclassical population transfer model, and demonstrate that this measurement is temperature sensitive with a statistical sensitivity to the fractional temperature uncertainty of 0.09 , corresponding to 26 K at room temperature. This represents a calibration-free SI-traceable temperature measurement, for which they calculate a systematic fractional temperature uncertainty of 0.006, corresponding to 2 K at room temperature when used as a primary temperature standard. They used 10^{6 85}Rb laser-excited Rydberg atoms (size ~ 100 nm) and laser-cooled to 0.5 mK in a MOT. The researchers make non-contact, calibration-free, 0-100 C, absolute temperature measurements by tracking atomic energy jumps induced by the emitted BBR over time. Every 300 ms, they load a new packet of ⁸⁵Rb atoms into the trap, cool them and excite them from the 5S energy level to the 32S Rydberg state. They then allow them to absorb black-body radiation from the surroundings for around 100 μs, causing some of the 32S atoms to change state. Then, they apply a strong, ramped electric field, ionizing the atoms. The higher energy states get ripped off easier than the lower energy states, so the electrons that were in each state arrive at the detector at a different time. In that way they get the readout indicating the population in each of the states. The researchers use this ratio to infer the spectrum of the BBR absorbed by the atoms and, then, the black body temperature. After pulsing a two-photon excitation to a Rydberg state, they wait 100 µs for BBR to couple from this Rydberg state to other states. Then, they sweep an electric field to selectively ionize Rydberg state atoms and collect the ions and stripped electrons using electron avalanche detectors. Each measurement takes 354 ms, consisting of 231 ms of experiment and 123 ms of dead time. The 3D MOT consists of three retroreflected laser beams ( 20 MHz detuned from the D2 line with 80 mW of power in a 1-cm beam radius) and two coils in an anti-Helmholtz configuration. The current through the coils is controlled with an insulated-gate bipolar transistor which allows the field to be switched off in 300 µs. They estimate the cloud to contain 2×10⁶ atoms, of which 5400 participate in the measurement. After the trap is released, the atoms are excited to a Rydberg state via laser 1 (resonant to the D2 line with 9 mW in a 5-mm beam radius) and laser 2 (resonant on the 5S3/2→32S1/2 transition with 57 mW in a 5 mm beam radius, locked to a two-photon electromagnetically induced transparency in a reference cell). After the blackbody coupling time, ionization is performed with two electrodes placed 56 mm apart that are swept from 0 to 3 kV in 7µs, and the ions and their electrons are collected using CEM detectors). The current incident on the anode of the CEM is converted into a voltage using a transimpedance amplifier with a gain of 10³ V/A and recorded on a scope.

For more information: Phys.org, January 23 (2025); Physicsworld, February 2 (2025); Phys. Rev. Res., January 23 (2025) page L012020.

Topological electronic crystals in TBLG:   an international group lead by researchers from the University of British Columbia in Vancouver, BC and the University of Washington in Seattle, WA has identified topological electronic crystal states in 2D twisted bilayer–trilayer graphene. They report signatures of a generalized version of the anomalous Hall effect driven by the moiré potential. The crystal forms at a band filling of one electron per four moiré unit cells (ν = 1/4) and quadruples the unit-cell area, coinciding with an integer quantum anomalous Hall effect. The Chern number of the state is tunable, and it can be switched reversibly between +1 and −1 by electric and magnetic fields. Several other topological electronic crystals arise in a low magnetic field, originating from ν = 1/3, 1/2, 2/3 and 3/2. The quantum geometry of the interaction-modified bands is expected to be very different from that of the original parent band.

For more information: Nature, January 22 (2025) page 1084; Phys.org, January 22 (2025).

WEEK OF JANUARY 20, 2025 [No. 1611]

High-fidelity long molecular entanglement demonstrated:   researchers at Durham in Durham have used rotationally magic-wavelength optical tweezers to create a controlled stable environment that supports long-lived (≈ 1 s) coherence between entangled ultracold polar molecules. They prepared two-molecule Bell states, using dipolar spin exchange and directed microwave excitation, with fidelities 0.924 (+0.013/-0.016) and 0.76 (+0.03/-0.04), respectively, limited by detectable leakage errors. When correcting for these errors, the fidelities were 0.976 (+0.014/-0.016) and 0.93 (+0.03/-0.05), respectively. This despite the Hz-scale interactions at their 2.8 μm particle spacing. They have shown that the second-scale entanglement lifetimes are limited solely by these errors. The speed and fidelity of their Bell-state preparation may be improved by changing the confinement of the molecules to access smaller separations. Transferring the molecules into a magic-wavelength optical lattice should give access to sub-µm separations and increased molecular confinement, resulting in increased interaction strengths with reduced noise.

For more information: Nature, January 15 (2025) page 827; Phys.org, January 15 (2025).

²⁵²Rf nucleus produced and decay measured:   researchers at the GSI in Darmstadt have discovered the shortest-lived superheavy nucleus, from the most neutron deficient ₁₀₄Rf isotope, at the boundary of the stability island in the sea of unstable superheavy nuclei. They report the discovery of ²⁵²Rf with ground state fission half-life 60(+90 / −30) ns, shorter than the previous minimum for spontaneously fissioning nuclei, thus, expanding the range of half-lives of the known superheavy nuclei by about 2 orders of magnitude. The researchers utilized an isomeric state with inverted fission stability for the measurement. The results here confirm a smooth onset of decreasing ground-state spontaneous fission half-lives in the neutron-deficient Rf isotopes toward the isotopic border of 10 fs (boundary determined as the time needed to form an atomic shell). The island of stability predicted in the 60's has been confirmed with the observation of increasing half-lives in the heaviest currently known nuclei as the predicted next magic number of 184 neutrons is approached. The short-lived ²⁵²Rf was synthesized in a gas recoil separator and guided to the detection system in its high-K isomeric state ^252mRf (for which they measured a half-life of 13(+4 / −3) μs) taking advantage of inverted fission-stability where excited states are more stable than the ground state. The researchers used an intense pulsed beam of ⁵⁰Ti available at the GSI/FAIR UNILAC accelerator to fuse Ti nuclei with ²⁰⁴Pb nuclei on a target foil. They used four different beam energies that resulted in excited ²⁵⁴Rf, that emits either one neutron to leave ²⁵³Rf or two neutrons to leave ²⁵²Rf. These isotopes were separated in the TransActinide Separator and Chemistry Apparatus TASCA. After a flight of 3.5 m (flight-time ≈ 0.6 µs), those were implanted into a Si detector that registered their implantation as well as their subsequent decay. The large beam energies used here favored the production of ²⁵²Rf over ²⁵³Rf. In total, 27 atoms of ²⁵²Rf decaying by fission with half-life 13 µs were detected. The electrons emitted after the implantation of the isomer ^252mRf in its decay to the ground state, were detected using a home-made fast digital data acquisition system. In all the three registered cases, a subsequent fission followed within 250 ns. From these data, a half-life of 60 ns was deduced for the ground state of ²⁵²Rf, making it the shortest-lived superheavy nucleus currently known. It was determined that almost all the 13-µs span belonged to the decay of the excited isomeric state in the ²⁵²Rf nucleus whose existence allowed the measurement of the 60-ns ground-state fission because the excited state survived the time-of-flight of the separator *so the ground state appeared and decayed in the detector rather than in the separator). In future experimental campaigns, the researchers plan the measurement of isomeric states with inverted fission stability in the next heavier element ₁₀₆Sg to further map the isotopic border of the stability island.

For more information: Phys.org, January 15 (2024); Physics, January 14 (2025); Phys. Rev. Lett., January 14 (2025) page 022501.

WEEK OF JANUARY 13, 2025 [No. 1610]

Fractional excitons observed:   researchers at Brown University in Providence, RI have observed excitons in the fractional quantum Hall regime. They used a bilayer graphene sandwiching an insulating hBN layer to control the movement of electrical charges and generate excitons under a high magnetic field. Some of the excitons arise from the pairing of fractionally charged particles and have non-bosonic properties that are different from fermions and anyons as well. The researchers present transport signatures of excitonic pairing in the fractional quantum Hall effect states. By probing the composition of these excitons and their impact on the underlying wavefunction, they discovered two new types of quantum phases of matter. One of those can be viewed as the fractional counterpart of the exciton condensate at a total filling of 1, whereas the other involves a more unusual type of exciton that obeys non-bosonic quantum statistics. The researchers will next study how these fractional excitons interact and whether their behavior can be controlled.

For more information: Nature, January 8 (2025) page 327; Phys.org, January 8 (2025).

Proximity ferroelectricity detected:   researchers in Penn State University at University Park, PA have detected proximity ferroelectricity in a non-ferroelectric polar material induced by one or more adjacent ferroelectric materials (wurtzite ferroelectric heterostructures). Proximity ferroelectricity enables polarization reversal in wurtzites without the chemical or structural disorder that accompanies elemental substitution. They had previously developed a ferroelectric material, Mg-substituted ZnO thin films. The ZnO has desirable properties, but it is not ferroelectric by itself. Adding Mg makes the material ferroelectric but degrades properties like heat dissipation during device operation and the ability to transmit light over very long distances. Using proximity ferroelectricity, the researchers found they could turn pure ZnO ferroelectric by stacking it with a ferroelectric material like the Mg-substituted ZnO thin films. The ZnO here can exhibit polarization reversal in its pure state. The ferroelectric layer can be just 3% of the total volume of the stack, meaning the vast majority is material with the most-desired properties. The ferroelectric, or switching layer, can be placed on the top or bottom or as an isolated internal layer. The researchers observed proximity ferroelectricity in oxide nitride and combined nitride-oxide systems, suggesting that there is a generic mechanism involved. The non-ferroelectric layers here are AlN and ZnO, whereas the ferroelectric layers are Al_1−xB_xN, Al_1−xSc_xN and Zn_1−xMg_xO. The layered structures include nitride–nitride, oxide–oxide and nitride–oxide stacks that feature two-layer (asymmetric) and three-layer (symmetric) configurations. Ferroelectric switching in both layers is validated by polarization hysteresis, anisotropic chemical etching, second harmonic generation, piezo response force microscopy, electromechanical testing and atomic resolution polarization orientation imaging in real space by STEM. The researchers present a physical switching model in which antipolar nuclei originate in the ferroelectric layer and propagate towards the internal non-ferroelectric interface. The domain wall leading edge produces elastic and electric fields that extend beyond the interface at close proximity, reducing the switching barrier in the non-ferroelectric layer, and allowing complete domain propagation without breakdown. DFT calculations of polymorph energies, reversal barriers and domain wall energies support this model.

For more information: Nature, January 8 (2025) page 574; Phys.org, January 8 (2025).

Time-domain oscillations between distant on-chip spins probed:   researchers at TU Delft in Delft have demonstrated coherent interaction between two semiconductor electron spin qubits 250 μm apart, using a superconducting resonator coupled to two gate-defined double dots. The separation is several orders of magnitude larger than for the commonly used direct interaction mechanisms in this platform. The researchers here demonstrate the time-domain control of a dot–resonator–dot system and realize two-qubit iSWAP oscillations between distant spin qubits. The two qubits are encoded in single-electron spin states and they are coupled via a 250-μm-long superconducting NbTiN on-chip resonator. The resonator is also used for dispersively probing the spin states. They demonstrate operations on individual spin qubits at the flopping-mode operating point and characterize the corresponding coherence times. They realize iSWAP oscillations between the two distant spin qubits in the dispersive regime. They study how the oscillation frequency varies with spin–cavity detuning, spin–photon coupling strength and frequency detuning between the two spin qubits, and compare the results with theoretical simulations. The researchers operate the system in a regime in which the resonator mediates a spin–spin coupling via virtual photons. Their observations are consistent with iSWAP oscillations between the distant spin qubits, and suggest that entangling operations are possible in 10 ns. The fabricated device was characterized by recording the microwave transmission from the input port via the resonator to the output port. The researchers initialized one spin in the ground state and the other in the excited state. When they activated the interaction between these spins, the two qubits transferred their quantum states back and forth. When one spin transitions to the ground state, the other simultaneously transitions to the excited state, and vice versa. After previous spectroscopic measurements relying on coherent spin-photon interactions, the researchers observed time-domain oscillations here. The researchers plan to increase the quality factor of the oscillations and study time-domain oscillations between each of the spins and real photons in the resonator in the form of vacuum Rabi oscillations

For more information: Physics, January 7 (2025); Nat. Phys., December 9 (2024).

WEEK OF JANUARY 6, 2025 [No. 1609]

No electronic correlation at twist angle 4.4° in dichalcogenide bilayers:   an international group lead by researchers at the University of Groningen in Groningen has used nano-ARPES to investigate structural relaxation in small angle twisted bilayer WS₂ and found electronic behavior inconsistent with theory predictions of collective behavior. They present here a systematic nano-ARPES investigation of bulk, single-layer, and twisted bilayer samples with a small twist angle (4.4°). The experimental results are compared with theoretical calculations based on DFT along the high-symmetry directions. The electronic band structure measurements suggest a structural relaxation occurring at twist angle 4.4° and the formation of large, untwisted bilayer regions replacing most of the twisted area with the twisted bilayer partially reverting to a lower-energy, untwisted configuration.

For more information: Phys.org, December 30 (2024); Phys. Rev. Mat., December 26 (2024) page 124004.

Spin-orbit coupled superconducting electrons:   researchers at the University of Minnesota have proposed that in certain materials, pair spin–orbit interaction (PSOI) is strong enough to engender unconventional superconductivity. They analyzed the PSOI arising from Coulomb interaction in a class of materials that exhibit spin–orbit coupling associated with a strong Rashba effect. This effect has been studied for decades, owing to the possibility of creating spin-polarized currents of electrons without the need to apply a magnetic field. The Rashba effect can arise in a crystal lacking inversion symmetry, where spin-up and spin-down electrons split into different conduction bands. PSOI can induce p-wave superconducting order without the need for attraction mediator. Depending on the sign and strength of the PSOI coupling, two distinct superconducting phases emerge in 3D systems, analogous to the A and B phases observed in superfluid ³He. In contrast, 2D systems exhibit order parameter like p^x ± iq^y, leading to time-reversal-invariant topological superconductivity. A sufficiently strong PSOI can induce ferromagnetic ordering. It is associated with a deformation of the Fermi surface, which eventually leads to a Lifshitz transition from a spherical to a toroidal Fermi surface, with a number of experimentally observable signatures. In pure Rashba materials, ferromagnetism and p-wave superconductivity may coexist. This state resembles the A₁ phase of ³He, yet it may avoid nodal points due to the toroidal shape of the Fermi surface. Their calculations show that the PSOI is strong in the considered Rashba materials and can induce electrons to pair up and produce a superconducting state. Although the pairing symmetry differs in 2D and 3D, in both cases it has odd parity, meaning that the system would be an unconventional superconductor. Such a state would be disrupted by modest concentrations of impurities and could be detectable in ultrapure samples at 100's mK.

For more information: Physics, January 2 (2025); Phys. Rev. B, January 2 (2025) page 035104.

NOTE: previous Research News (since WEEK OF MARCH 1, 1994 [No. 1], around the time when the Quantum Cascade Lasers were demonstrated at AT&T Bell Laboratories in Murray Hill, N.J., as promising MIR solid-state room temperature sources that would enable laser spectroscopy in the spectral region where fundamental rotational-vibrational transitions of most molecules take place) not posted.