Author(s): Sankar Das Sarma and Haining Pan
Motivated by a recent breakthrough transport experiment [Phys. Rev. B 107, 245423 (2023)] in Majorana nanowires, we theoretically investigate local and nonlocal transport in Majorana nanowires in various disorder regimes, correlating the transport properties with the corresponding local and total de…
[Phys. Rev. B 108, 085415] Published Thu Aug 10, 2023
Two-dimensional (2D) transition-metal dichalcogenides (TMDC) are considered highly promising platforms for next-generation optoelectronic devices. Owing to its atomically thin structure, device performance is strongly impacted by a minute amount of defects. Although defects are usually considered to be disturbing, defect engineering has become an important strategy to control and design new properties of 2D materials. Here, we produce single S vacancies in a monolayer of MoS$_2$ on Au(111). Using a combination of scanning tunneling and atomic force microscopy, we show that these defects are negatively charged and give rise to a Kondo resonance, revealing the presence of an unpaired electron spin exchange coupled to the metal substrate. The strength of the exchange coupling depends on the density of states at the Fermi level, which is modulated by the moir\'e structure of the MoS$_2$ lattice and the Au(111) substrate. In the absence of direct hybridization of MoS$_2$ with the metal substrate, the S vacancy remains charge-neutral. Our results suggest that defect engineering may be used to induce and tune magnetic properties of otherwise non-magnetic materials.
Nature, Published online: 04 August 2023; doi:10.1038/d41586-023-02481-0
Social media is abuzz with chatter about the material, but some scientists are pushing back on the hype.Author(s): Valentin Crépel, Daniele Guerci, Jennifer Cano, J. H. Pixley, and Andrew Millis
Robust attraction and low-energy symmetry properties in transition metal dichalcogenide twisted bilayers may produce topologically protected superconductivity.
[Phys. Rev. Lett. 131, 056001] Published Tue Aug 01, 2023
Nature Materials, Published online: 03 August 2023; doi:10.1038/s41563-023-01622-0
Magnetic imaging reveals that a transport current flows in the interior of Cr-(Bi,Sb)2Te3 samples within the quantum anomalous Hall regime, contrary to the common assumption of current flow along the sample edge.Nature, Published online: 02 August 2023; doi:10.1038/s41586-023-06330-y
Quantum oscillations in the three-dimensional topological semimetal CoSi are reported, where selected oscillation frequencies have no corresponding extremal Fermi surface cross-sections, representing instead oscillations of the quasiparticle lifetime.Nature, Published online: 02 August 2023; doi:10.1038/d41586-023-02016-7
Sandwich compounds are molecules in which two planar molecular rings sandwich a metal ion ‘filling’ between them. The chemistry of these compounds has been extended by the assembly of nano-rings from 18 identical sandwich-type building blocks.Author(s): Valentin Leeb and Johannes Knolle
The Fermi surface — the manifold of gapless excitations forming due to Pauli’s famous exclusion principle— determines all electronic properties of metals. In 1952 Lars Onsager discovered how to measure a Fermi surface by studying the response of a metallic material as a function of an applied magnetic field. In fact, observables like electrical resistivity or the magnetization oscillate as a function of inverse field. Onsager’s relation forms the basis for our understanding of electronic properties of metals and is used in many experimental labs around the world. Here, the authors find that, in the presence of strong interactions between electrons, Onsager’s relation can be violated and they provide the first rigorous calculations of this effect. In general, solving for the emergent Landau levels of a strongly interacting material in a magnetic field is a hard problem. The methodological progress made here is enabled by concentrating on an exactly soluble model with infinite-range interactions. This research establishes the importance of inter Landau level interactions for understanding correlated materials in magnetic fields.
[Phys. Rev. B 108, 085106] Published Thu Aug 03, 2023
Nature, Published online: 27 July 2023; doi:10.1038/d41586-023-02438-3
Marc Tessier-Lavigne’s departure makes overworked researchers ponder: how do we prevent misconduct in our own labs?Optical driving of materials has emerged as a versatile tool to control their properties, with photo-induced superconductivity being among the most fascinating examples. In this work, we show that light or lattice vibrations coupled to an electronic interband transition naturally give rise to electron-electron attraction that may be enhanced when the underlying boson is driven into a non-thermal state. We find this phenomenon to be resonantly amplified when tuning the boson's frequency close to the energy difference between the two electronic bands. This result offers a simple microscopic mechanism for photo-induced superconductivity and provides a recipe for designing new platforms in which light-induced superconductivity can be realized. We propose a concrete setup consisting of a graphene-hBN-SrTiO$_3$ heterostructure, for which we estimate a superconducting $T_{\rm c}$ that may be achieved upon driving the system.
Full-shell nanowires are hybrid nanostructures consisting of a semiconducting core encapsulated in an epitaxial superconducting shell. When subject to an external magnetic flux, they exhibit the Little-Parks (LP) phenomenon of flux-modulated superconductivity, an effect connected to the physics of Abrikosov vortex lines in type-II superconductors. We show theoretically that full-shell nanowires can host subgap states that are a variant of the Caroli-de Gennes-Matricon (CdGM) states in vortices. These CdGM analogs are shell-induced Van Hove singularities in core subbands. We elucidate their structure, parameter dependence and behavior in tunneling spectroscopy through a series of models of growing complexity. Using microscopic numerical simulations, we show that CdGM analogs exhibit a characteristic skewness towards higher flux values inside non-zero LP lobes resulting from the interplay of three ingredients. First, the orbital coupling to the field shifts the energy of the CdGM analogs proportionally to the flux and to their generalized angular momentum. Second, CdGM analogs coalesce into degeneracy points at flux values for which their corresponding radial wavefunctions are threaded by an integer multiple of the flux quantum. And third, the average radii of all CdGM-analog wavefunctions inside the core are approximately equal and are controlled by the electrostatic band bending at the core/shell interface. As the average radius moves away from the interface, the degeneracy points shift towards larger fluxes from the center of the LP lobes, causing the skewness. This analysis provides a transparent interpretation of the nanowire spectrum that allows to extract microscopic information by measuring the number and skewness of CdGM analogs. Moreover, it allows to derive an efficient Hamiltonian of the full-shell nanowire in terms of a modified hollow-core model at the average radius.
Nature, Published online: 25 July 2023; doi:10.1038/d41586-023-02361-7
Large language models mimic human chatter, but scientists disagree on their ability to reason.Moir\'e systems made from stacked two-dimensional materials host novel correlated and topological states that can be electrically controlled via applied gate voltages. We have used this technique to manipulate Chern domains in an interaction-driven quantum anomalous Hall insulator made from twisted monolayer-bilayer graphene (tMBLG). This has allowed the wavefunction of chiral interface states to be directly imaged using a scanning tunneling microscope (STM). To accomplish this tMBLG carrier concentration was tuned to stabilize neighboring domains of opposite Chern number, thus providing topological interfaces completely devoid of any structural boundaries. STM tip pulse-induced quantum dots were utilized to induce new Chern domains and thereby create new chiral interface states with tunable chirality at predetermined locations. Theoretical analysis confirms the chiral nature of observed interface states and enables the determination of the characteristic length scale of valley polarization reversal across neighboring tMBLG Chern domains. tMBLG is shown to be a useful platform for imaging the exotic topological properties of correlated moir\'e systems.
Nature, Published online: 19 July 2023; doi:10.1038/s41586-023-06264-5
The electronic states in three-dimensional crystals such as graphite can be tuned by a superlattice potential occurring at the interface with crystallographically aligned hexagonal boron nitride.Author(s): Yasen Hou, Fabrizio Nichele, Hang Chi, Alessandro Lodesani, Yingying Wu, Markus F. Ritter, Daniel Z. Haxell, Margarita Davydova, Stefan Ilić, Ourania Glezakou-Elbert, Amith Varambally, F. Sebastian Bergeret, Akashdeep Kamra, Liang Fu, Patrick A. Lee, and Jagadeesh S. Moodera
A superconducting strip allows more superconducting current to flow in one direction than in the other—achieving a stronger diode effect than previous devices.
[Phys. Rev. Lett. 131, 027001] Published Thu Jul 13, 2023
We investigate the role of the Bloch functions and superconducting gap symmetries on the formation and properties of impurity-induced resonances in a two-dimensional superconductor, and elucidate their manifestation in scanning tunneling spectra. We use and extend a recently developed scattering approach, conveniently formulating the results in terms of the phase shifts of electron scattering off the impurity. We find that the discrete subgap states in a nodeless-gap superconductor are insensitive to the potential scattering phase shift (common for the two spin species) if time-reversal symmetry (TRS) is preserved. The independence of potential scattering is exact for $s$-wave superconductors. It remains an accurate approximation over a broad range of subgap energies when the gap function breaks the lattice point symmetry, except for a narrow region below the gap edge. Breaking of TRS makes potential scattering capable of creating spin-degenerate subgap states, which may be further split by spin-dependent scattering. In nodal-gap superconductors, impurity-induced resonances are broadened by coupling to the quasiparticle continuum. We identify the conditions allowing for the formation of narrow resonances. In addition to finding the energy spectrum, we evaluate the spin-resolved differential conductance for all of the considered symmetries and gap structures.
Nature, Published online: 12 July 2023; doi:10.1038/d41586-023-02139-x
Analysis of which researchers publish, get credit, move around, get funding, collaborate and receive citations shows how deeply ingrained the bias against women is.Author(s): Alexandre Gourmelon, Elric Frigerio, Hiroshi Kamata, Lukas Lunczer, Anne Denis, Pascal Morfin, Michael Rosticher, Jean-Marc Berroir, Gwendal Fève, Bernard Plaçais, Hartmut Buhmann, Laurens W. Molenkamp, and Erwann Bocquillon
High-frequency transport in the edge states of the quantum spin Hall (QSH) effect has rarely been explored, though it could cast light on the scattering mechanisms taking place therein. Here we report on the measurement of the plasmon velocity in topological HgTe quantum wells both in the QSH and qu…
[Phys. Rev. B 108, 035405] Published Wed Jul 12, 2023
Nature, Published online: 12 July 2023; doi:10.1038/s41586-023-06195-1
A scalable approach is provided for preparing and verifying intermediate-scale genuine entanglement on a 66-qubit superconducting quantum processor.Nature, Published online: 12 July 2023; doi:10.1038/s41586-023-06097-2
Spectroscopic measurements of individual rare-earth ion electron spins are performed by detecting their microwave fluorescence, with the method coming close to practical single-electron spin resonance at millikelvin temperatures.Nature Physics, Published online: 10 July 2023; doi:10.1038/s41567-023-02104-5
One-dimensional chains of magnetic adatoms on the surface of a superconductor have been claimed to host topological states. Now, this idea is extended to two-dimensional systems.Nature Materials, Published online: 29 June 2023; doi:10.1038/s41563-023-01583-4
The study of point defects in non-metallic crystals has become relevant for an increasing number of materials applications. Progress requires a foundation of consistent definitions and terminology. This Comment clarifies the underlying definitions of point defects, encourages the correct use of relative charge for their description and emphasizes their recognition as quasiparticles.Author(s): Ying-Ming Xie and K. T. Law
An orbital field-driven Fulde–Ferrell (FF) pairing state can be driven by the orbital effects of in-plane magnetic fields (different from the conventional Zeeman effects-driven FF state), such a pairing makes possible a giant and gate-tunable superconducting diode effect.
[Phys. Rev. Lett. 131, 016001] Published Wed Jul 05, 2023
Author(s): Xiao-Feng Chen, Wenchen Luo, Tie-Feng Fang, Yossi Paltiel, Oded Millo, Ai-Min Guo, and Qing-Feng Sun
Recently, electron transport along chiral molecules has been attracting extensive interest and a number of intriguing phenomena have been reported in recent experiments, such as the emergence of zero-bias conductance peaks in the transmission spectrum upon the adsorption of single-helical protein on…
[Phys. Rev. B 108, 035401] Published Wed Jul 05, 2023
Author(s): Hang Yan, Ze-Xian Deng, Jia-Qi Fan, Xue-Qing Yu, Xiao-Peng Hu, Can-Li Song, Xu-Cun Ma, and Qi-Kun Xue
Superconducting infinite-layer Sr1−xEuxCuO2 films at optimal doping (x∼0.15) have been epitaxially grown on SrTiO3(001) substrates with oxide molecular beam epitaxy. By combining x-ray diffraction and transport measurements, we have established a narrow window of growth conditions [i.e., ozone press…
[Phys. Rev. Materials 7, 074802] Published Thu Jul 06, 2023
Author(s): Warren E. Pickett
Superconductivity, discovered in 1911 and first theoretically understood in 1957, remains a fascinating phenomenon for reasons both fundamental and applied. Reliably calculating the critical temperature of a given material, and even more so predicting it, turned out to be a considerable challenge. This Colloquium explains how theoretical developments have led to increasingly reliable predictions that have culminated in the discovery of the hydride materials that display superconductivity under high pressure at temperatures just shy of room temperature.
[Rev. Mod. Phys. 95, 021001] Published Fri Apr 07, 2023
Nature Physics, Published online: 08 July 2019; doi:10.1038/s41567-019-0576-7
Potential Majorana bound states are seen in the vortex cores of a transition metal dichalcogenide. The properties of the superconductor mean that the bound states are highly anisotropic, and can appear at higher temperatures than other materials.There is presently a tremendous activity around the field of topological superconductivity and Majorana fermions. Among the many questions raised, it has become increasingly important to establish the topological or non-topological origin of features associated with Majorana fermions such as zero-bias peaks. Here, we compare in-gap features associated either with isolated magnetic impurities or with magnetic clusters strongly coupled to the atomically thin superconductor Pb/Si(111). We study this system by means of scanning tunneling microscopy and spectroscopy (STM/STS). We take advantage of the fact that the Pb/Si(111) monolayer can exist either in a crystal-ordered phase or in an incommensurate disordered phase to compare the observed spectroscopic features in both phases. This allows us to demonstrate that the strongly resolved in-gap states we found around the magnetic clusters in the disordered phase of Pb have a clear topological origin.
Dr.jens.bredeEssentially the same observation we have for CuPC/Gr/Fe...
Author(s): Giulia Avvisati, Pierluigi Gargiani, Pierluigi Mondelli, Francesco Presel, Alessandro Baraldi, and Maria Grazia Betti
We investigate the magnetic response of a spin interface constituted by MnPc molecules adsorbed on graphene/Co and its robustness against thermal fluctuations by x-ray magnetic circular dichroism. Element-selective hysteresis loops reveal a remarkable antiferromagnetic coupling between MnPc and Co t...
[Phys. Rev. B 98, 115412] Published Thu Sep 06, 2018