Theory seminar, Thursday, November 22, 2018, Kapitza Institute, 11:30 am Vladimir Krasnov (Stockholm University, Sweden) Josephson and nonJosephson emission from Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} mesa structures Mesa structures made of Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} hightemperature superconductor represent stacks of atomic scale intrinsic Josephson junctions. When voltage is applied to such mesas, they can generate various types of waves (photons, phonons, polaritons, magnons, plasmons) in a variety of different ways. In this talk I will overview both Josephson and nonJosephson mechanisms of emission, including the standard acJosephson effect for emission of electromagnetic waves [1], segnetoelectric effect for emission of phonons and polaritons [2] and nonequilibrium quasiparticle relaxation and recombination for emission of any type of bosons, having strong electronboson interaction and participating in pairing [3]. Those effects are important both for applied research, e.g., creation of tunable, compact, continuous wave and monochromatic THz source with a frequency span in the whole THz gap region and beyond 0.115 THz [1,2], and for fundamental understanding of the mechanism of pairing in hightemperature superconductors [3]. 
Scientific Council of the Landau Institute, Friday, November 23, 2018, Landau Institute, 11:30 am P. A. Ioselevich, P. M. Ostrovsky, Ya. V. Fominov Mesoscopic supercurrent fluctuations in diffusive magnetic Josephson junctions We study the supercurrent in quasionedimensional Josephson junctions with a weak link involving magnetism, either via magnetic impurities or via ferromagnetism. In the case of weak links longer than the magnetic pairbreaking length, the Josephson effect is dominated by mesoscopic fluctuations. We establish the supercurrentphase relation (CPR) along with statistics of its sampledependent properties in junctions with transparent contacts between leads and link. High transparency gives rise to the inverse proximity effect, while the direct proximity effect is suppressed by magnetism in the link. We find that all harmonics are present in the CPR. Each harmonic has its own sampledependent amplitude and phase shift with no correlation between different harmonics. Depending on the type of magnetic weak link, the system can realize a \varphi_0 or \varphi junction in the fluctuational regime. Full supercurrent statistics is obtained at arbitrary relation between temperature, superconducting gap, and the Thouless energy of the weak link. 
Scientific Council of the Landau Institute, Friday, November 23, 2018, Landau Institute, 11:30 am Konstantin Tikhonov Statistics of eigenstates near the localization transition on random regular graphs Dynamical and spatial correlations of eigenfunctions as well as energy level correlations in the Anderson model on random regular graphs (RRG) are studied. We consider the critical point of the Anderson transition and the delocalized phase. In the delocalized phase near the transition point, the observables show a broad critical regime for system sizes below the correlation volume and then cross over to the ergodic behavior. Eigenstate correlations allow us to visualize the correlation length that controls the finitesize scaling near the transition. The criticaltoergodic crossover is very peculiar, since the critical point is similar to the localized phase, whereas the ergodic regime is characterized by very fast diffusion which is similar to the ballistic transport. In particular, the return probability crosses over from a logarithmically slow variation with time in the critical regime to an exponentially fast decay in the ergodic regime. We find a perfect agreement between results of exact diagonalization and those resulting from the solution of the selfconsistency equation obtained within the saddlepoint analysis of the effective supersymmetric action. We show that the RRG model can be viewed as an intricate limit of the Anderson model in spatial dimensions. 
Laboratory building, room 122
Moscow Institute of Physics and Technology
Dolgoprudny, Russia
contact email address: nanotheory@phystech.edu (head M.V.Feigel'man, deputy head I.V.Zagorodnev)
Research topics


Scientific Council of the Landau Institute, Friday, November 16, 2018, Landau Institute, 11:30 am Ya.V. Fominov Poverkhnostnyi impedans na diffuznoi granitse kiral'nogo pvolnovogo sverkhprovodnika Vychislena lokal'naya kompleksnaya provodimost' i obuslovlennyi eyu poverkhnostnyi impedans na diffuznoi granitse kiral'nogo pvolnovogo sverkhprovodnika. Imenno kiral'noe pvolnovoe sostoyanie schitaetsya naibolee veroyatnym v sverkhprovodyashchem rutenate strontsiya Sr_{2}RuO_{4}. Ono anizotropnoe i pri etom polnost'yu shchelevoe (modul' parametra poryadka fiksirovan, a faza zavisit ot napravleniya). My rassmatrivaem otklik na vneshnee elektromagnitnoe pole kak na podshchelevykh, tak i na nadshchelevykh chastotakh. Izucheny anomal'nye osobennosti poverkhnostnogo impedansa, svyazannye s generatsiei vblizi granitsy nechetnykh po chastote sverkhprovodyashchikh korrelyatsii (sostoyanie tipa sverkhprovodimosti Berezinskogo). Teoreticheskie rezul'taty sopostavleny s izmereniyami poverkhnostnogo impedansa Sr_{2}RuO_{4}, provedennymi v IFTT. Nablyudaetsya kachestvennoe soglasie teorii i eksperimenta. 
Scientific Council of the Landau Institute, Friday, November 16, 2018, Landau Institute, 11:30 am Ya.V. Fominov Sverkhprovodyashchii spinovyi klapan v sistemakh so splavom Geislera Provedeno teoreticheskoe soprovozhdenie eksperimentov po izmereniyu effekta sverkhprovodyashchego spinovogo klapana v sisteme tipa FFS (gde F — ferromagnetik, S — sverkhprovodnik). Effekt sostoit v tom, chto kriticheskaya temperatura T_{c} sistemy zavisit ot vzaimnoi orientatsii namagnichennostei dvukh ferromagnetikov. V eksperimente v kachestve srednego F sloya byl vzyat splav Geislera Co_{2}Cr_{1x}Fe_{x}Al, i eto pozvolilo usilit' effekt (raznost' T_{c} pri parallel'noi i antiparallel'noi orientatsii) po sravneniyu s ranee issledovannymi sistemami s zhelezom. Znak effekta zavisit ot tolshchiny sloya. Teoriya ob'yasnyaet poluchennye rezul'taty. Usilenie effekta okazyvaetsya svyazano s umen'shennoi velichinoi obmennogo polya v splave Geislera. 
Shmidtovskii seminar po sverkhprovodimosti, Thursday, November 15, 2018, MISiS, auditoriya B607, 5:00 pm Tim Duty (University of New South Wales, Australia), Karin Cedergren, Sergey Kafanov, Roger Ackroyd and Jared H. Cole Magneticfieldinduced parity effect in insulating Josephson junction chains We report the experimental manifestation of evenodd parity effects in the transport characteristics of insulating Josephson junction chains, which occur as the superconducting gap is suppressed by applied magnetic fields at millikelvin temperatures. The primary signature is a nonmonotonic dependence of the critical voltage, Vc, for the onset of charge transport through the chain, with the parity crossover indicated by a maximum of Vc at the parity field B*, We also observe a distinctive change in the transport characteristics across the parity transition, indicative of Cooperpair dominated transport below B*, giving way to singleelectron dominated transport above B*, For fields applied in the plane of the superconducting aluminum films, the parity effect is found to occur at the field, B*, such that the superconducting gap equals the singleelectron charging energy, Δ(B*)=EC. On the contrary, the parity effect for perpendicularly applied fields can occur at relatively lower fields, B*⊥≃ 2Φ0/AI, depending only on island area, AI. In this case, the parity effect occurs in sync with formation of the singlevortex state of the islands in the chain. Our results suggest a novel explanation for the insulating peak observed in disordered superconducting films and onedimensional strips patterned from such films, which occurs at a finite magnetic field. 