Quantum Materials Seminar

semester, 2018

Tuesday, January 30th 2018
3:30 pm:
Speaker: Damjan Pelc, University of Minnesota
Subject: New ways to learn about quantum materials
Refreshments will be served at the meeting so don't forget to bring your favorite mug.

I will discuss two unusual experimental techniques currently being developed for the study of quantum materials: nonlinear magnetic response and uniaxial pressure. They can be used to detect and modify the fundamental symmetries of materials, with great potential for new insights. In particular, I will examine the symmetry properties of nonlinear magnetic susceptibility, with applications in the study of chiral superconductors. Furthermore, I will present a novel approach to uniaxial pressure experiments, which can easily be combined with various other techniques to investigate the effects of broken structural symmetries.

Tuesday, February 13th 2018
3:30 pm:
Speaker: Maria Navarro Gastiasoro, University of Minnesota
Subject: "Superconductivity in Strontium Titanate"

Tuesday, February 27th 2018
3:30 pm:
Speaker: Samuel Lederer, MIT
Subject: High temperature superconductivity and strange metal behavior near a metallic quantum critical point

It has long been conjectured that quantum critical points (QCPs) are at the root of some of the most fascinating phenomena in the solid state, including the high temperature superconductivity and “strange metal” behavior of cuprate superconductors. Though much progress has been made in the theory of QCPs, those which occur in metals (and are likely relevant to the high temperature superconductors) are still poorly understood despite more than four decades of effort. Using Quantum Monte Carlo techniques, my collaborators and I have performed the first numerically exact simulations of a model which realizes a metallic QCP towards an Ising nematic ordered phase. I will discuss our results, which include numerous phenomena already observed in experiment, and comment on future avenues towards a solution of this difficult and rich problem in quantum statistical mechanics.

Faculty Host: Rafael Fernandes

Tuesday, March 20th 2018
3:30 pm:
Speaker: Laxman Raju Thoutam and Sajna Hameed.
Subject: Novel Electronic and Magnetic Properties in Rare-Earth Titanates: YTiO3 & NdTiO3.

Tuesday, April 3rd 2018
3:30 pm:
Speaker: John Dewey and Joseph Batley, Chemical Engineering and Material Science
Subject: Integration of perovskites into non-local spin valves for the study of spin transport in oxides“

Friday, April 6th 2018
3:35 pm:
Speaker: Kenji Ishii, Synchrotron Radiation Research Center (SPring-8), Japan
Subject: Momentum-resolved charge and spin excitations in cuprate superconductors

In the last two decades, energy resolution of resonant inelastic x-ray scattering (RIXS) has been significantly improved, and RIXS is now established as a momentum-resolved spectroscopy using synchrotron radiation x-rays. Since the beginning of RIXS, cuprate superconductors have been intensively studied. In addition to the interest of superconductivity at the high transition temperature and related phenomena, such as pseudogap and a competing phase with charge order, doped cuprates are important and suitable for the study of the electronic structure of the doped Mott insulator. This is because relatively simple theoretical models with a few orbitals are applicable to describe the electronic structure near the Fermi energy. I will present charge and spin excitations in cuprates observed with RIXS at Cu K-, Cu L3- and O K-edges focusing on the energy range from eV to sub-eV. In this range, charge and spin excitations show characteristic momentum dependence with respective energy scale of hopping energy of electron (t) and exchange interaction of spin (J).

Faculty Host: Martin Greven

Tuesday, April 17th 2018
3:30 pm:
Speaker: Zach Anderson and Yang Tang, University of Minnesota
Subject: Doping dependence of the antiferromagnetic response of HgBa2CuO4+δ

Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and of the pseudogap phenomena exhibited by the cuprates. Neutron scattering measurements of the antiferromagnetic response have been reported for a number of cuprates, but our study of structurally simple HgBa2CuO4+δ (Hg1201) shows several features distinct from what has been found in other materials. In particular, at most dopings and temperatures we see a gapped Y-shaped magnetic dispersion in contrast to the X-shaped response seen in other cuprates. We will discuss our ongoing efforts to understand the doping dependence of the magnetic spectrum in Hg1201.

Friday, April 27th 2018
2:00 pm:
Speaker: Masaaki Matsuda, ORNL
Subject: Magnetic correlations in the vicinity of the superconducting state in CrAs and MnP
Please note time and date change for this seminar. This week only.

CrAs and MnP exhibit superconductivity under pressure with a maximum transition temperature of ~2 K at 2 GPa and ~1 K at 8 GPa, respectively. Since Cr and Mn have the spin degree of freedom, elucidating the magnetic contribution to the superconductivity is crucial to understand the pairing mechanism. A helical structure is the magnetic ground state at ambient pressure in both materials. We performed neutron scattering studies in both materials under pressure. With applying pressure, the helicity and magnetic moment of the helical structure gradually change in CrAs [1], whereas MnP shows a more complicated phase diagram [2]. Most importantly, we found that both materials show helical structure in the vicinity of the superconducting phase, although the directions of the propagation vectors are different. We also studied the chemical pressure effect on static and dynamic magnetic properties in CrAs [1]. The results suggest a coupling between the magnetism and the superconductivity.

[1] M. Matsuda et al., submitted to PRX.
[2] M. Matsuda et al., Phys. Rev. B 93, 100405(R) (2016).

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