Forum DQMP

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Day / Time
Date(s) - 27/10/2015
13 h 00 min - 14 h 00 min

Category


Tuesday, October 27th 2015 – 13h00

Auditoire Stückelberg – Ecole de physique

 

Coffee and tea will be available from

12h50 at the entrance of the Auditoire

 

Interplay of magnetism and pressure induced superconductivity

in CeAu2Si2

Gernot W. Scheerer (group of Prof. Jaccard)

 

Although known for many years (huge γ-value of CeAl3 in 1975, superconductivity in CeCu2Si2 in

1979), Heavy Fermions are still intensely studied, since they reunite some of the most interesting

features of solid state physics, e.g.: strongly correlated electron systems, quantum criticality, non-fermiliquid

behavior, and unconventional superconductivity. I will give a short introduction to heavy-fermion

superconductors, focusing on the CeM2X2-familiy (M = transition metal, X = Si/Ge). Recently, we

discovered pressure-induced superconductivity (SC) deep inside the antiferromagnetic phase of

CeAu2Si2 (pc ~ 22.5 GPa), where superconductivity sets in at 11.8 GPa [Ren et al. Phys. Rev. X, 4,

031055 (2014)]. This large overlap of magnetism and superconductivity is markedly different from all

previous cases! I will present our newest resistivity, ac-specific heat, and thermopower measurements

on CeAu2Si2 under high-pressure. The obtained p-T-phase diagram shows a new kind of complex

interplay between magnetism, pressure-induced quantum criticality and the emergence of partial and

bulk superconductivity.

 

Laser-induced phenomena in quantum magnets

Shintaro Takayoshi (group of Prof. Giamarchi)

Quantum magnets show rich quantum many-body physics such as various kinds of phase transitions,

topological orders, and spin liquids. It is an important task to find a scheme to realize nontrivial

coherent states in such systems, and we propose a way to control quantum states by applying laser to

materials. The electric and magnetic components of laser are coupled to magnets through the Zeeman

coupling and, in multiferroics, electric polarization. We consider laser as a time-periodic external field.

Using the Floquet theory, the original time-dependent system is mapped to an effective static

Hamiltonian with a synthetic field, which gives rise to nontrivial quantum states. In this presentation, we

focus on a laser application to quantum antiferromagnets and multiferroics. As for antiferromagnets, we

demonstrate a net magnetization can be manipulated by circularly polarized laser. We can even realize

dynamical magnetization curves with a technique of frequency modulation of laser. In the case of

multiferroic materials, the direction of Dzyaloshinskii-Moriya interaction is effectively modified through

the coupling between spin chirality and electric polarization.

 

Forum Committee : L. Foini, C. Lichtensteiger, N. Ubrig (20.10.2015)

Réalisation : Sur Mesure concept