Condensed Matter Seminars

At the interface between electron- and hole-doped curates

Speaker: 
Marcel Hoek, University of Twente
Event Date and Time: 
Thu, 2013-07-18 14:00 - 15:00
Location: 
AMPEL 311
Local Contact: 
Elfimov, Ilya
Intended Audience: 
Graduate

We report on the fabrication of in-plane ramp-edge structures between c-axis oriented superconducting Nd1.85Ce0.15CuO4 (NCCO) and La1.85Sr0.15CuO4 (LSCO). The ab-plane contact allows us to explore p/n physics in the rich phase diagram of the cuprates.

Detecting Non-Abelian Anyons by Charging Spectroscopy

Speaker: 
Gilad Ben-Shach
Event Date and Time: 
Tue, 2013-06-18 14:00 - 15:00
Location: 
AMPEL 311
Local Contact: 
Joshua Folk
Intended Audience: 
Graduate

Observation of non-Abelian statistics for the charge e/4 quasiparticles in the v=5/2 fractional quantum Hall state remains an outstanding experimental problem. The non-Abelian statistics are linked to the presence of additional low energy states in a system with localised quasiparticles, and hence an additional low-temperature entropy. Recent experiments, which detect changes in the number of quasiparticles trapped in a local potential well as a function of an applied gate voltage, provide a possibility for measuring this entropy, if carried out over a suitable range of temperatures.

Quantum sensing and engineering with nitrogen vacancy centers in diamond

Speaker: 
Steven Bennett, Harvard University
Event Date and Time: 
Mon, 2013-06-03 12:00 - 13:00
Location: 
Hennings 318
Local Contact: 
Sarah Burke
Intended Audience: 
Graduate

 

Nitrogen vacancy centers (NVs) in diamond constitute solid state "artificial atoms" and provide a natural setting to study the interface between condensed matter physics and quantum optics.  In this talk I will discuss how coherent control of one or many NVs can be used for quantum sensing and to design interesting many-body spin Hamiltonians.

Anisotropic topological insulators

Speaker: 
Roland Hayn form the Université d'Aix-Marseille
Event Date and Time: 
Tue, 2013-04-16 03:30 - 16:30
Location: 
AMPEL 311
Local Contact: 
Maria Pylaeva
Intended Audience: 
Graduate

Density functional calculations predict metacinnabar (beta-HgS) to be a strong topological insulator with a highly anisotropic Dirac cone [1]. Similar results were found for Ag2Te [2]. The anisotropy has the advantage of a high spin relaxation time in contrast to the isotropic case. Surface modifications may change the anisotropy of the Dirac cone.

[1] F. Virot, R. Hayn, M. Richter, J van den Brink, Phys. Rev. Lett. 106, 236806 (2011).
[2] W. Zhang et al, Phys. Rev. Lett. 106, 156808 (2011).

Backscattering Between Helical Edge States via Dynamic Nuclear Polarization

Speaker: 
Adrian Del Maestro, University of Vermont
Event Date and Time: 
Thu, 2013-05-16 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Ian Affleck
Intended Audience: 
Graduate

We describe how the non-equilibrium spin polarization of one dimensional helical edge states at the boundary of a two dimensional topological insulator can dynamically induce a polarization of nuclei via the hyperfine interaction. When combined with a spatially inhomogeneous Rashba coupling, the resulting steady state polarization of the nuclei produces backscattering between the topologically protected edge states leading to a reduction in the conductance which persists to zero temperature.

Ligand hole effects in transition-metal compounds with small charge-transfer energy

Speaker: 
Takashi Mizokawa (Department of Complexity Science and Engineering, University of Tokyo)
Event Date and Time: 
Thu, 2013-03-07 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Maria Pylaeva
Intended Audience: 
Graduate

 

Integer anomalous quantum Hall effect and fractional excitations in itinerant magnets.

Speaker: 
Armin Rahmanisisan, Los Alamos National Laboratory
Event Date and Time: 
Thu, 2013-05-02 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Ian Affleck
Intended Audience: 
Graduate

 

The interplay of chiral magnetic ordering and itinerant electrons can lead to the emergence of anomalous integer quantum Hall effect. We show that the topological defects in the magnetic textures of such systems can have fractional electric charge and anyonic exchange statistics. We further demonstrate that such quantized Hall effect may appear in the absence of quasi-long-range magnetic order, i.e., in spin-ice-like systems. The magnetic monopoles of such systems carry a fluctuating electric dipole.

 

Classification of topological insulators and superconductors in the presence of reflection symmetry

Speaker: 
Ching-Kai Chiu (University of Illinois)
Event Date and Time: 
Thu, 2013-04-25 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Marcel Franz
Intended Audience: 
Graduate

We discuss a topological classification of insulators and superconductors in the presence of both (non-spatial) discrete symmetries in the Altland-Zirnbauer classification and spatial reflection symmetry in any spatial dimensions. By using the structure of bulk Dirac Hamiltonians of minimal matrix dimensions and explicit constructions of topological invariants, we provide the complete classification, which still has the same dimensional periodicities  with the original Altland-Zirnbauer classification.

Visualizing heavy fermions emerging in a quantum critical Kondo lattice

Speaker: 
Eduardo da Silva Neto (Princeton University)
Event Date and Time: 
Mon, 2013-02-18 14:00 - 15:00
Location: 
AMPEL 311
Local Contact: 
Andrea Damascelli
Intended Audience: 
Graduate

In solids containing elements with f orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass. This is one of the key concepts in the physics of correlated electronic states and is fundamental to the mechanism of unconventional superconductivity in such systems.

Layer-by-layer entangled spin-orbital texture of the topological surface state in Bi2Se3

Speaker: 
Jason Zhu (UBC)
Event Date and Time: 
Thu, 2013-02-07 14:00 - 15:00
Location: 
Hennings 318
Intended Audience: 
Graduate

With their spin-helical metallic surface state, topological insulators (TIs) define a new class of materials with strong application potential in spintronics. Technological exploitation depends on the degree of spin polarization of the topological surface state (TSS), assumed to be 100% in phenomenological models. Yet in Bi2Se3, an archetypical TI material, spin- and angle-resolved photoemission spectroscopy (S-ARPES) detects a spin polarization ranging from 20 to 85%, a striking discrepancy which undermines the applicability of real TIs.

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