News and posts

Poster Session

Poster 39	Andrzej Ptok	Polish Academy of Sciences	Artificial separation of trivial and topological superconducting domains
Poster 40	Raquel Queiroz	Weizmann Institute of Science	Splitting the Hinge Mode of Higher-Order Topological Insulators
Poster 41	Peter Rickhaus	ETH Zürich	Charge Density waves in Twisted Double Bilayer Graphene
Poster 42	Vudtiwat Ngampruetikorn Wave	Dept. of Physics, Northwestern University USA	Anomalous Thermal Hall Effect in Chiral Superconductors
Poster 43	Alexander Shnirman	Karlsruhe Institute of Technology	Current–phase relation in a topological Josephson junction: Andreev bands vs. scattering states
Poster 44	Anastasiia Skurativska	University of Zurich	Atomic limit and inversion-symmetry indicators for topological superconductors
Poster 45	Ben Stoddart-Stones	University of Cambridge	Competing proximity effect and spin accumulation in superconducting spin valves
Poster 46	Shu-Ichiro Suzuki	Nagoya University	Anomalous inverse proximity effect in unconventional-superconductor junctions
Poster 47	Hidemitsu Takahashi	Kyoto University	121/123Sb-NMR/NQR studies on the superconducting line-nodal material CaSb2
Poster 48	Ryo Taniguchi	Kyoto University	Biaxial dilatometer using fiber Bragg grating for low temperatures
Poster 49	Marco Valentini	IST AUSTRIA	Non-topological zero bias peaks in full-shell nanowires induced by flux tunable Andreev states
Poster 50	Hannes Weisbrich	University Konstanz	Second Chern Number and Non-Abelian Berry Phase in Topological Superconducting Systems
Poster 51	Terufumi Yamaguchi	YITP, Kyoto University	Microscopic Theory of Topological Hall effect on the Surface of Topological Insulator
Poster 52	Yuki Yamazaki	Nagoya University	Majorana Electric Quadrupole Response in Topological Crystalline Superconductors
Poster 53	Guang Yang	University of Cambridge	Exploring spin supercurrent transport in lateral spin valve
Poster 54	Rikizo Yano	IMaSS, Nagoya University	Superconducting Proximity Effect on a Magnetic Topological Insulator Controlled by Magnetization
Poster 55	Victor Yarzhemsky	Institute of General & Inorganic Chemistry of RAS	Space-group approach to the wavefunction of a Cooper pair. Applications to topological superconductors UTe2 and Sr2RuO4
Poster 56	Lingfeng Zhang	University of Antwerp	Electronic properties of emergent topological defects in chiral p-wave superconductors and topological phase transitions in small disks
Poster 57	Alireza Akbari	MPI for the Chemical Physiks of Solids, Dresden	Gapped Dirac cones and spin texture in thin film topological insulator

Poster Session

Poster 20	Pablo Garcia Campos	CNRS - Nèel Institute	SQUID imaging of the intermediate state of the type-I superconductor PdTe2
Poster 21	Mayo Kawaguchi	Department of physics, Graduate School of Science	Discovery of superconductivity in the line-nodal material CaSb2
Poster 22	Jinkwon Kim	Seoul National University	Superconducting Sr2RuO4 thin film growth achieved by interface engineering
Poster 23	Graham Kimbell	University of Cambridge, Dept of Materials Science	Two-channel anomalous Hall effect in SrRuO3
Poster 24	Raffael Klees	FB Physik, University Konstanz	Microwave Spectroscopy Reveals the Quantum Geometric Tensor of Topological Josephson Matter
Poster 25	Eun Kyo Ko	Seoul National University	Oxygen Vacancy Engineering for Highly Tunable Ferromagnetic Properties: A Case of SrRuO3 Ultrathin Film with a SrTiO3 Capping Layer
Poster 26	Shingo Kobayashi	RIKEN CEMS	Majorana vortex zero modes in superconducting topological crystalline insulators
Poster 27	Michael Koblischka	Shibaura Institute of Technology, Tokyo	Magic-angle superconducting graphene and the Roeser-Huber formula
Poster 28	Seung Hun Lee	Seoul National University	Odd–Parity Spin–Triplet Superconductivity in Antiferromagnetic Metals Lacking Effective Time-Reversal Symmetries
Poster 29	Zijin Lei	solid state physics lab, ETH Zurich	Electronic Transport in InSb Quantum Wells
Poster 30	Hisakazu Matsuki	University of Cambridge	Spin-injection into spin-split superconductors via spin pumping
Poster 31	Giordano Mattoni	Kyoto University	Imaging the current-driven metal–insulator transition in Ca2RuO4
Poster 32	Maria Teresa Mercaldo	Dipartimento di Fisica, Universit di Salerno, Ita	Designing Nonstandard Andreev-Bound-State Spectra in Majorana Devices
Poster 33	Andreas Michelsen	University of St Andrews	Andreev reflection through tunneling in a spinless chiral edge state
Poster 34	Archana Mishra	MagTop, IFPAN, Warsaw, Poland	Dynamical torques from Shiba states in s-wave superconductors
Poster 35	Itsuki Miyazaki	Tokyo Institute of Technology	Superconductivity in SrAuSi3 with noncentrosymmetric crystal structure probed by μSR
Poster 36	Seishiro Ono	The University of Tokyo	Z2-enriched symmetry indicators for topological superconductors in the 1651 magnetic space groups
Poster 37	Bo Peng	University of Cambridge	Topological phonons in oxide perovskites controlled by light
Poster 38	Annika Stellhorn	Forschungszentrum Jülich GmbH, JCNS-2	Interplay of proximity effects in Nb/FePd heterostructures: domain-superconductivity, spin-triplet Cooper pair generation, and the impact on the ferromagnet

Topological Nature of High Temperature Superconductivity

Valerii Vinokour

An underlying mechanism of the high temperature superconductivity (HTS) and the nature of the adjacent phases remains the biggest mystery of condensed matter physics. It is believed that the key to understanding of HTS lies in revealing the origin of the enigmatic properties of the pseudogap state that settles in the underdoped region between the superconducting transition temperature Tc and the pseudogap temperature T* > Tc. The experiments indicate that the pseudogap state is a distinct thermodynamic phase that exhibits metallic transport, magnetoelectric effect and the nematicity. We develop a unified theory that offers a quantitative description of the pseudogap phase properties and describes the observed phase diagram. The proposed mechanism of the superconductivity is the emergence of the condensate of dyons, the composite particles carrying both electric and magnetic charge, in our case the Cooper pair bound with the magnetic monopole. In the HTS phase, the dyon condensate coexists with the fundamental Cooper pair condensate and the elevated Tc results from the stabilizing effect of the monopole condensate. We show that in the pseudogap phase charged magnetic monopole condensate realizes the oblique confinement of Cooper pairs. The universality of the HTS phase diagram for different materials reflects the unique topological mechanism responsible for formation of the emerging phases. Our findings provide a topological reason for the high critical temperature in HTS.

One-dimensional moiré charge density wave in the hidden order state of URu2Si2 induced by fracture

Edwin Herrera

URu2Si2 is a heavy fermion system which crystallizes in a tetragonal structure and where superconductivity emerges inside the misterious hidden order phase. The latter consists of a still unknown type of order that appears together with a strong entropy reduction below 17.5 K. URu2Si2 becomes superconducting below 1.5 K. The hidden order phase is characterized by dynamical spin modes at q0=(0 0 1) and q1=(0.6 0 0). These quench into an antiferromagnetic order under pressure (q0=(0 0 1)) and at high magnetic fields (q1=(0.6 0 0)). Here I will show recent Scanning Tunneling Microscopy experiments (STM) at very low temperatures (0.1 K). I will report on the discovery of a charge modulation with a wavevector that is a moiré combination of the atomic lattice periodicity and q1, produced by fracturing the crystal in presence of the dynamical spin mode at q1. Our results suggest that charge interactions are a fundamental ingredient that competes with hidden order in URu2Si2 and advance controlled fracture as powerful means to obtain ground states derived from strong electronic correlations [1]. Furthermore, I will show results at surfaces with large amounts of atomically flat steps showing the U fourfold lattice. There we find a new heavy fermion 2D-electron gas type of surface state with an effective mass 17 times the free electron mass. We discuss lateral quantization of such 2D heavy electrons and the interaction of the surface band with bulk superconductivity.

[1] E. Herrera, et. al., One-dimensional moire charge density wave in the hidden order state of URu2Si2 induced by fracture, arXiv:2003.07881v2 (2020).

Poster Session

Poster 1	Uriel Aceves	Forschungszentrum Jülich	In-gap states emerging from magnetic nanostructures deposited on superconductors
Poster 2	Armando Aligia	Centro Atomico Bariloche, Argentina	Tomography of zero-energy end modes in topological superconducting wires
Poster 3	Daniil Antonenko	Skoltech / Landau Institute	Mesoscopic conductance fluctuations and noise in disordered Majorana wires
Poster 4	Ryo Araki	Department of Physics, Kyoto University	Anisotropy of the upper critical field of Sr2RuO4 under in-plane magnetic field and current
Poster 5	Olga Arroyo	Instituto de Ciencia de Materiales de Madrid	One-Dimensional Moiré Superlattices and Magic Angle Physics in Collapsed Chiral Carbon Nanotubes
Poster 6	Thomas Baker	Institut quantique (UniversitÈ de Sherbrooke)	Role of canting and depleted-triplet minima in superconducting spin valve structures
Poster 7	Harry Bradshaw	University of Cambridge	Infinite Magnetoresistance at a Rare Earth Ferromagnet / Superconductor Interface
Poster 8	David Cavanagh	The University of Otago	Robustness of unconventional s-wave superconducting states against disorder
Poster 9	Ashley Cook	Max-Planck-Institut fuer Physik komplexer Systeme	Topological skyrmion phases of matter
Poster 10	Folkert de Vries	ETH Zürich, Laboratory of Solid State Physics	Interlayer scattering in twisted double bilayer graphene
Poster 11	Juan Carlos Estrada Saldaña	University of Copenhagen	Non-trivial effects in “trivial” hybrid nanowire-superconductor devices
Poster 12	Remko Fermin	Universiteit Leiden	Spontaneous emergence of Josephson junctions in homogeneous rings of single-crystal Sr2RuO4
Poster 13	Victor Fernandez-Becerra	Institute of Physics, Polish Academy of Sciences	Topological charge, spin and heat transistor
Poster 14	Yuri Fukaya	Nagoya University	Orbital tunable 0-π transitions in Josephson junctions with noncentrosymmetric topological superconductors
Poster 15	Shreenanda Ghosh	Technical University of Dresden, Germany	Manipulation of time reversal symmetry breaking superconductivity in Sr2RuO4 by uniaxial stress
Poster 16	Ruben Gracia	Instituto de Nanociencia y Materiales de Aragûn	Robust Weak-Antilocalization effect in Bi2Se3 thin films
Poster 17	Vadim Grinenko	TU Dresden	s+is superconductivity in Ba1-xKxFe2As2
Poster 18	Yajian Hu	Kyoto University	Detection of hole pockets in the candidate type-II Weyl semimetal MoTe2 from Shubnikov-de Haas quantum oscillations
Poster 19	Shota Kanasugi	Kyoto University	Multiorbital odd-frequency pairing in a ferroelectric superconductor SrTiO3

Second Order Topological Superconductivity: Majorana and parafermion corner states

Jelena Klinovaja

Recently, a lot of interest has been raised by the generalization of conventional TIs/TSCs to so-called higher order TIs/TSCs. While a conventional d-dimensional TI/TSC exhibits (d − 1)-dimensional gapless boundary modes, a d-dimensional n-th order TI/TSC hosts gapless modes at its (d − n)-dimensional boundaries. In my talk, I will consider a Josephson junction bilayer consisting of two tunnel-coupled two-dimensional electron gas layers with Rashba spin-orbit interaction, proximitized by a top and bottom s-wave superconductor with phase difference φ close to π [1-3]. In the presence of a finite weak in-plane Zeeman field, the bilayer can be driven into a second order topological superconducting phase, hosting two Majorana corner states (MCSs). If φ=π, in a rectangular geometry, these zero-energy bound states are located at two opposite corners determined by the direction of the Zeeman field. If the phase difference φ deviates from π by a critical value, one of the two MCSs gets relocated to an adjacent corner. As the phase difference φ increases further, the system becomes trivially gapped. The obtained MCSs are robust against static and magnetic disorder.

In the second part of my talk, I will switch from non-interacting systems [4,5], in which one neglects effects of strong electron-electron interactions, to interacting systems and, thus, to exotic fractional phases. I will show that this is indeed possible and explicitly construct a two-dimensional (2D) fractional second-order TSC. I will consider a system of weakly coupled Rashba nanowires in the strong spin-orbit interaction (SOI) regime. The nanowires are arranged into two tunnel-coupled layers proximitized by a top and bottom superconductor such that the superconducting phase difference between them is π. In such a system, strong electron- electron interactions can stabilize a helical topological superconducting phase hosting Kramers partners of Z_2m parafermion edge modes, where m is an odd integer determined by the position of the chemical potential. Furthermore, upon turning on a weak in-plane magnetic field, the system is driven into a second- order topological superconducting phase hosting zero-energy Z_2m parafermion bound states localized at two opposite corners of a rectangular sample.

References

[1] Y. Volpez, D. Loss, and J. Klinovaja, Phys. Rev. Lett. 122,126402 (2019) 
[2] K. Plekhanov, M. Thakurathi, D. Loss, and J. Klinovaja, Phys. Rev. Research 1, 032013(R) (2019) 
[3] K. Plekhanov, N. Müller, Y. Volpez, D. M. Kennes, H. Schoeller, D. Loss, and J. Klinovaja, arXiv:2008.03611 
[4] K. Laubscher, D. Loss, and J. Klinovaja, Phys. Rev. Research 1, 032017(R) (2019)
[5] K. Laubscher, D. Loss, and J. Klinovaja, Phys. Rev. Research 2, 013330 (2020)

Two-dimensional Topological Superconductivity

Eun-Ah Kim

One could envision different strategies for designing topological superconductivity. One strategy would be to restrict the phase space in the kinetic energy by manipulating the band structure. Another strategy would be to restrict the pairing interaction. I will our proposals following each of these strategies. For the band-structure manipulation, I will discuss the prediction of p-wave superconductivity in p-doped TMD's with intermediate interaction. I will also discuss the competition for the surface state among multiple topological orders in FeSeTe. For the strategy of manipulating pairing interaction, I will discuss our proposal of using a metal-quantum paramagnet heterostructure.

Fingerprints of Majorana modes beyond the zero-bias conductance peak

Satoshi Ikegaya

The unambiguous detection of Majorana bound states (MBSs) in topological superconductors has been a central topic of condensed matter physics for recent years. So far, the presence of MBSs was demonstrated experimentally in a number of topologically nontrivial superconducting systems. In this connection, clear evidences of Majorana bound states are only obtained by the detection of zero-bias conductance peaks in tunneling transport measurements. In recent years, it became clear that various additional signatures of Majorana modes need to be investigated in order to complete our understanding.
In our presentation, we summarize two unambiguous fingerprints which can act as a ‘smoking gun’evidence. First we study the anomalous nonlocal conductance due to chiral Majorana edge states in a superconductor/ferromagnet hybrid as shown in Fig. 1(a). We obtain the important result that the chiral nature of the Majorana edge states causes an anomalously long-range and chirality-sensitive nonlocal transport in this device. This, in turn, enables us to identify conclusively the moving direction and further properties of the chiral Majorana edge states [1]. Secondly, we propose a novel experiment for achieving the first experimental observation of the anomalous proximity effect caused by Majorana bound states. In particular, we discuss the differential conductance of a semiconductor/superconductor hybrid as shown in Fig. 1(b), which contains a planar topological Josephson junction realized in recent experiments. The conductance spectrum changes drastically through the topological phase transition because the Majorana bound state appearing only in the topologically nontrivial phase can penetrate into the dirty normal segment and form the resonant transmission channel there [2]. In general, our results allow contrasting singlet and triplet superconductivity employing properties of Majorana modes beyond zero bias peaks.

[1] S. Ikegaya, Y. Asano, and D. Manske, Phys. Rev. Lett. 123, 207002 (2019)
[2] S. Ikegaya, S. Tamura, D. Manske, and Y. Tanaka, arXiv: 2007.12888 (2020)

Odd-frequency pairing in topological superconductors

Yukio Tanaka

It is known that odd-frequency pairing ubiquitously presents in superconductor junctions [1]. Especially, in the presence of zero energy surface Andreev bound state (ZESABS) realized in topological superconductors, the odd-frequency pairing is amplified near the surface or interface. One of the remarkable property generated by odd-frequency pairing is anomalous proximity effect in diffusive normal metal (DN) / superconductor junction where quasiparticle density of states in DN has a zero energy peak (ZEP) of LDOS due to the penetration of odd-frequency spin-triplet s-wave pairing [2,3]. It has been shown that proximity coupled nano-wire junction [4] is an idealistic system to study anomalous proximity effect due to odd-frequency triplet-s wave pairing [5].
We have further clarified the relation between induced odd-frequency pairing and the bulk quantity defined by Green’s function[6]. Odd-frequency Cooper pairs with chiral symmetry emerging at the edges are a useful physical quantity. We have shown that the odd-frequency Cooper pair amplitudes can be expressed by a winding number extended to a nonzero frequency and can be evaluated from the spectral features of the bulk. We have found that the odd-frequency Cooper pair amplitudes are classified into two categories: the amplitudes in the first category have the singular functional form proportional to 1/z (where z is a complex frequency) that reflects the presence of ZESABS, whereas the amplitudes in the second category have the regular form proportional to z.
Recently, we have found that the presence of ZESABS generates new type of thermopower.
We have shown that the thermoelectric effect in ferromagnet / superconductor junctions can be entirely dominated by ingap Andreev reflection processes. Consequently, the electric current from a temperature bias changes sign in the presence of ZESABS and resulting odd-frequency pairing [7].

[1]Y. Tanaka, M. Sato and N. Nagaosa, J. Phys. Soc. Jpn. 81 011013 (2012)
[2]Y. Tanaka and A.A. Golubov, Phys. Rev. Lett. 98 037003 (2007)
[3]Y. Tanaka, A.A. Golubov, S. Kashiwaya, and M. Ueda, Phys. Rev. Lett. 99 037005 (2007); Y. Tanaka, Y. Tanuma, and A. A. Golubov, Phys. Rev. B 96 054552 (2007)
[4]Y. Tanaka and S. Kashiwaya, Phys. Rev. B 70 012507 (2004)
[5]R. M. Lutchyn, J. D. Sau, and S. Das Sarma, Phys. Rev. Lett. 105, 077001 (2010), Y. Oreg, G. Refael, and F. von Oppen, Phys. Rev. Lett. 105, 177002 (2010)
[6]Y. Asano and Y. Tanaka, Phys. Rev. B 87 104513 (2013)
[7]S. Ta mura, S. Hoshino and Y. Tanaka, Phys. Rev. B 99 , 184512 (2019)
[8]T. Savander , S. Tamura, C. Flindt, Y. Tanaka and P. Burset , arXiv: 2008.00849

Propagation and interference of d-wave superconducting pairs in graphene

Javier Villegas

Following earlier work in which we demonstrated the Klein-like tunneling of d-wave superconducting paints intro graphene [1], here we present experiments that show the longrange preparation of d-wave correlations in that material. For this, we fabricated devices that behave as a proximitized Fabry-Pérot cavitiy, where d-wave Andreev pairs interferences are produced. The interferences manifest themselves in series of pronounced conductance oscillations analogous to those produced by De Gennes-Saint James resonances in conventional superconductor/metal junctions. Their observation imply that the d-wave Andreev pairs propagate over distances of a few hundred nm in the CVD graphene used for the experiments [2]. We will end up by discussing ongoing experiments in applied magnetic field, which also produces an intriguing series of conductance oscillations in the superconducting state of the junctions.

[1] D. Perconte, F. A. Cuellar, C. Moreau-luchaire, M. Piquemal-Banci, R. Galceran, P. R. Kidambi, M.-B. Martin, S. Hofmann, R. Bernard, B. Dlubak, P. Seneor, and J. E. Villegas, Nat. Phys. 14, 25 (2018)
[2] D. Perconte, K. Seurre, V. Humbert, C. Ulysse, A. Sander, J. Trastoy, V. Zatko, F. Godel, P. R. Kidambi, S. Hofmann, X. P. Zhang, D. Bercioux, F. S. Bergeret, B. Dlubak, P. Seneor, and J. E. Villegas, Phys. Rev. Lett. 125, 87002 (2020)