Dicke Candidate Seminar | Zurab Guguchia | "Probing the superconducting and magnetic properties of strongly correlated and topologically non-trivial materials" | Jadwin 303

Mon, Jan 8, 2018, 4:00 pm
Location: 
Jadwin Room 303
Speaker(s): 

In this talk a selection of some results of the hydrostatic pressure and impurity effects on structural, magnetic
and superconducting properties in the stripe phase of La214 cuprates [1] and in the Weyl semimetal phase of
MoTe2 [2] will be presented.
Cuprate high-temperature superconductors (HTSs) have complex phase diagrams with multiple competing
ordered phases. Understanding to which degree charge, spin, and superconducting orders compete or coexist is
paramount for elucidating the microscopic pairing mechanism in the cuprate HTSs. We discovered a novel nonmagnetic
Zn impurity and hydrostatic pressure effects on the static spin-stripe order in the La214 cuprates.
Remarkably, it was found that in these systems the spin-stripe ordering temperature Tso is extremely sensitive to
impurities within a CuO2 plane. Moreover, Tso is suppressed in the same manner as the superconducting transition
temperature Tc by Zn impurities. We also observed the same pressure evolution of both Tc and Tso, while there is
an antagonistic pressure evolution of magnetic volume fraction and superfluid density. These results suggest that
the existence of the stripe order requires intertwining with the SC pairing correlations.
Topological metals or Weyl semimetals, in which low energy excitations are Weyl fermions have attracted a lot
of attention, making this research area one of the hottest in modern physics. In its orthorhombic Td polymorph,
MoTe2 is a type-II Weyl semimetal, where the Weyl fermions emerge at the boundary between electron and hole
pockets. Understanding the superconductivity in Td-MoTe2, which was proposed to be topologically non-trivial,
is of eminent interest. I will present the results of high-pressure muon spin rotation experiments probing the
temperature-dependent magnetic penetration depth in Td-MoTe2. A substantial increase of the superfluid density
and a linear scaling with the superconducting critical temperature Tc is observed under pressure. Moreover, the
superconducting order parameter in Td-MoTe2 is determined to have 2-gap s-wave symmetry. Considering the
strong suppression of Tc in MoTe2 by disorder, we suggest that topologically nontrivial s+- state is more likely to
be realized in MoTe2 than the topologically trivial s++ state.