[Landau ITP Seminars] Thursday 27.10.2025 - ITP/CAS Colloquium

[Stanislav Apostolov]

Уважаемые коллеги!

На онлайн коллоквиум по теоретической физике в четверг 27.11 будут 
заслушаны 2 доклада:

1) Ordered and Tunable Majorana-Zero-Mode Lattice in Iron-Based 
Superconductors

в 10:00

Hong-Jun Gao (Institute of Physics, Chinese Academy of Sciences)

Majorana zero-modes (MZMs) are spatially-localized zero-energy 
fractional quasiparticles with non-Abelian braiding statistics. They are 
believed to hold great promise for topological quantum computation. By 
using low-temperature and strong-magnetic-field scanning tunneling 
microscopy/spectroscopy, a breakthrough of Majorana zero mode has been 
firstly achieved in a single material platform of high-Tc iron-based 
superconductor, FeTe0.55Se0.45. The mechanism of two distinct classes of 
vortices presented in this system was revealed, which directly tied with 
the presence or absence of zero-bias peak. We further found the Majorana 
conductance plateau in vortices. Both the extrinsic instrumental 
convoluted broadening and the intrinsic quasiparticle poisoning can 
reduce the conductance plateau value, and when extrinsic instrumental 
broadening is removed by deconvolution, the plateau nearly reaches a 
2e2/h quantized value. Moreover, we confirmed the existence of MZMs in 
the vortex cores of CaK-Fe4As4 and LiFeAs. Based on these works 
mentioned above, most recently, we have successfully achieved the 
large-scale, highly-ordered and tunable MZM lattice in strained LiFeAs. 
Notably, more than 90% of the vortices are topological and possess the 
characteristics of isolated MZMs at the vortex center, forming ordered 
MZM lattice with the density and the geometry tunable by external 
magnetic field. With decreasing the spacing of neighboring vortices, the 
MZMs start to couple with each other. This kind of materials combine the 
advantages of a simple material, high- Tc, large ratio of Δ/EF and etc. 
Our results show a great potential of MZMs in the application of 
topological quantum computation in the future.

Biography
Prof. Hong-Jun Gao obtained his Ph.D. from Peking University in 1994. He 
is now a Group Leader in Institute of Physics, an Academician of the 
CAS, and an Academician of the Developing-country Academy of Sciences 
(TWAS). From 1997 to 2000, he worked at the Oak Ridge National 
Laboratory (ORNL) as a Guest Scientist. He was the Scientific Secretary 
of the International Union of Vacuum Science, Technology, and 
Applications (IUVSTA) in the triennium 2004-2007, and the Chairman of 
the NSTD, IUVSTA (2010-2013). He served as an Associate Editor for Appl. 
Phys. Lett. From 2010 to 2018, and are editorial board members for 
several international journals. He was the Vice-President of the U-CAS 
and Chair of the U-CAS Advisory Committee of Sciences from 2014 to 2015. 
In the past years he visited several universities in the US as a 
Visiting Professor or Scientific Consultant.

His research interests focus on construction and physical properties of 
quantum nanostructures and scanning tunneling microscopy/spectroscopy 
(STM/STS). He has 8 international books/chapters, more than 500 journal 
publications including Science, Nature, Nature series, Phys. Rev. Lett., 
J. of Amer. Chem. Soc., Adv. Mater., and more than 120 invited talks. 
The total citation is more than 35000 and the H-index=95. His research 
works have been highlighted by the American Physical Society-physics, 
Physical Review Focus, Science News, Nature Materials, and Nature 
Nanotechnology, etc.

He was awarded several international Awards, including the "Humboldt 
Research Award" in 2010, the "OCPA AAA (Robert Prize)" in 2008 (OCPA: 
Overseas Chinese Physics Association; AAA: Achievement in Asia Award), 
and the "TWAS Prize in Physics 2009" (TWAS: Developing-country (Third 
World) Academy of Sciences). He also got a few top-level awards in 
China, for example, "Tan Kah Kee Science Awards on Mathematics and 
Physics 2018", "Science and Technology Awards of the Ho Leung Ho Lee 
2012", and "Outstanding Science and Technology Achievement Prize of the 
Chinese Academy of Sciences 2013".

2) Balancing an Inverted Pendulum Under Random Force: Statistics of the 
Never-Falling Trajectory
в 11:00

Mikhail A. Skvortsov (L.D. Landau Institute for Theoretical Physics, 
Russian Academy of Sciences)

Various fields of physics involve a class of problems related to 
minimization of a functional of an angular variable, which depends on a 
single coordinate, in the presence of a random force. The corresponding 
second-order differential equation of motion is unstable, making its 
solution a non-trivial numerical task. A paradigmatic model for this 
class of phenomena is finding the never-falling trajectory (NFT) of an 
inverted pendulum subjected to a time-dependent horizontal force (the 
Whitney problem).

We have shown that the Whitney problem, considered over the entire time 
axis, has a unique solution, and for the first time, we have raised the 
question of describing its statistical properties when averaged over an 
ensemble of random forces. For the white-noise random force, we 
construct a complete field-theoretical description of the statistics of 
the NFT, based in the the Parisi-Sourlas supersymmetric representation. 
The joint probability distribution function of the angle and its 
velocity is expressed via the solution of an auxiliary Fokker-Planck 
problem and found analytically in the limits of weak and strong noise. 
We also determine the Lyapunov exponent, describing the divergence of 
nearby solutions around the NFT.

Biography
Mikhail A. Skvortsov graduated from the Moscow Institute of Physics and 
Technology in 1995 and got his PhD in 1998. Since then, he has been 
continuously employed at the Landau Institute for Theoretical Physics. 
 From 2014 to 2021, he served as an Associate Professor at the Skolkovo 
Institute of Science and Technology. M. A. Skvortsov is a recognized 
specialist in the physics of disordered and superconducting systems. His 
key scientific contributions include explaining the giant fluctuation 
Nernst effect in superconductors, investigating ergodicity and 
localization on random regular graphs, developing the Keldysh action 
approach for disordered superconductors, describing the inhomogeneous 
state in dirty superconductors, constructing the theory of dynamical 
localization in quantum dots under periodic driving, characterizing the 
statistics of the never-falling trajectory in the random Whitney 
problem.

Zoom: 829 6586 0457, Passcode: 911242
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