CENTER FOR QUANTUM MATERIALS AND CONDENSED MATTER PHYSICS SEMINARS

NEWS: The CQM Distinguished Lecture series has been established  in the Fall of 2015 to bring to Stony Brook University the renown experts in the physics of quantum matter.

The lectures in this series will attract a broad audience of physicists from SBU and BNL,
and SBU graduate students.

October – November 2018

Oct
26
Fri
Michael Martin (Advanced Light Source, LBL) “SINS: Synchrotron Infrared Nano Spectroscopy extending into the far-IR”
Oct 26 @ 1:30 pm – 2:30 pm
Abstract: Scattering scanning near-field optical microscopy (s-SNOM) has emerged as a powerful imaging and spectroscopic tool for investigating nanoscale heterogeneities in biology, quantum matter, and electronic and photonic devices. However, many materials are defined by a wide range of fundamental molecular and quantum states at far-infrared (FIR) resonant frequencies currently not accessible by s-SNOM. Here we show ultrabroadband FIR s-SNOM nano-imaging and spectroscopy by combining synchrotron infrared radiation with a novel fast and low-noise copper-doped germanium (Ge:Cu) photoconductive detector [1]. This approach of FIR synchrotron infrared nanospectroscopy (SINS) extends the wavelength range of s-SNOM to 33µm (330 cm −1 , 10 THz), exceeding conventional limits [2] by an octave toward lower energies. We demonstrate this new nano-spectroscopic window by measuring elementary excitations of exemplary functional materials, including surface phonon-polariton waves and optical phonons in oxides and layered ultrathin van der Waals materials, skeletal and conformational vibrations in molecular systems, and the highly tunable plasmonic response of graphene.
Continued detector development in collaboration with NSLS-II will further extend the range of FIR SINS to ultimately bridge the energy gap with available THz s-SNOM sources, yet in a single nano-spectroscopy instrument. This work highlights the continued advantage of synchrotron radiation as an ultra-broadband coherent light source for near-field nano-spectroscopy, especially in the long wavelength regime where alternative low-noise, broadband, quasi-cw laser sources are not readily available.
References
[1] Khatib, Bechtel, Martin, Raschke, Carr,  ACS Photonics, 5(7), 2773–2779(2018).
[2] Bechtel, Muller, Olmon, Martin, Raschke, PNAS 111(20), 7191–7196 (2014).
Nov
2
Fri
Tyler M. Cocker (MSU)
Nov 2 @ 1:30 pm – 2:30 pm
Nov
30
Fri
Peter D. Johnson: Topology meets High Tc Superconductivity in the FeTe1-xSex family
Nov 30 @ 1:30 pm – 2:30 pm

Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973

Abstract

 

Low energy, laser-based ARPES with variable light polarization, including both linear and circularly polarized, is used to examine the Fe-based superconductor family, FeTe1-xSex.  At the center of the Brillouin zone we observe the presence of a Dirac cones with helical spin structure as expected for a topological surface state and as previously reported in the related FeTe0.55Se0.45.  These experimental studies are compared with theoretical studies that take account of the disordered local magnetic moments related to the paramagnetism observed in this system.  Indeed including the magnetic contributions in the theoretical description is necessary to bring the chemical potential of the calculated electronic band structure into alignment with the experimental observations.  In the bulk superconducting state for FeTe0.7Se0.3 the system appears to reflect the presence of some level of orbital selectivity in the pairing even though the system is in the tetragonal phase above and below the transition temperature Tc.  At the same time the topological state appears to acquire mass at the superconducting transition, possibly indicative of time reversal symmetry breaking.  These observations are discussed in detail.