CENTER FOR QUANTUM MATERIALS AND CONDENSED MATTER PHYSICS SEMINARS

During Fall 2020, seminars will be posted on this calendar and take place via Zoom. To join the mailing list and get the link, email Jennifer Cano (first name.lastname@stonybrook.edu)

The CQM Distinguished Lecture series has been established in the Fall of 2015 to bring to Stony Brook University the renowned 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.
Jun
5
Fri
JOURNAL CLUB: Matt Dawber (SBU)
Jun 5 @ 10:00 am – 11:00 am

Unlocking the secrets of growth and switching in ferroelectric multilayers using synchrotron x-ray diffraction

Powerful new capabilities at the NSLS-II synchrotron at Brookhaven National Laboratory have enabled us to perform a series of in-situ experiments that have allowed us to unlock important secrets about the growth and switching processes in ferroelectric multilayers. In one set of experiments, at 4-ID, the In-Situ and Resonant scattering beamline (ISR),  we perform x-ray diffraction during growth of sputtered ferroelectric multilayers and reveal that not only is the polarization intricately linked to crystal structure, also plays an important role in the growth process, influencing growth rates, relaxation mechanisms, electrical properties and domain structures. In a complementary set of experiments on the 11-ID, Coherent Hard X-Ray scattering (CHX) beamline, the high coherent flux at this beamline allows us to perform X-Ray Photon Correlation Spectroscopy measurements that monitor correlations between ferroelectric domain configurations as they are influenced by temperature and electric field stimuli. This method gives us an unprecedented view of the nanoscale arrangement of domains as a statistical ensemble as they are driven through thermal relaxation or switching events. Taken together, and combined with the extensive complimentary characterization we perform in our laboratory these experiments provide an unprecedented end-to-end window on to how strain, polarization and domain structure evolve into the complex configurations that generate much of the interest in these exciting materials.

Jun
12
Fri
JOURNAL CLUB: Dr. Kevin Cremin (UCSD) and Jeremy Lee-Hand (SBU)
Jun 12 @ 1:30 pm – 2:30 pm
Two talks!
1:30 pm -2:00 pm: Kevin Cremin (postdoc in Richard Averitt’s group at UCSD)
“Photo-enhanced metastable c-axis electrodynamics in stripe-ordered cuprate La_{1.885}Ba_{0.115}CuO_4″
The emergence of superconductivity in high-temperature cuprates arises out of a rich landscape of competing order. For example, stripe order can hoard the electrons needed to form Cooper pairs and establish superconductivity. Intriguingly, the complex interactions of such intertwined orders can be manipulated with light, where nonequilibrium dynamics alter the primacy of one order over another. Following photoexcitation of La2−xBaxCuO4 (x = 0.115) with near-infrared pulses, we observe a long-lived state that exhibits enhanced superconducting correlations well above the equilibrium superconducting transition temperature. Our analysis reveals that this metastable phase arises from a collapse of stripe order, providing an important demonstration of light-directed control in quantum materials.
2:00 pm -2:30 pm: Jeremy Lee-Hand (Ph.D. student in Cyrus Dreyer’s group)
First-principles study of molybdinate perovskite oxides
Perovskite oxides have a characteristic ABO3 structure that is able to accommodate a large number of different cations in the A and B locations. A relatively recently fabricated class of perovskites, are the molybdinates with B = Mo. We use first-principles calculations based on density-functional theory (DFT) plus Hubbard U to investigate the family of perovskite molybdenates: SrMoO3, PbMoO3, and LaMoO3 in order to determine their ground-state atomic and magnetic structures. We determine the dependence with the choice of U and interpret the ground-state structures in terms of unstable phonon modes.
Jun
19
Fri
Jigang Wang (Iowa State and Ames Lab)
Jun 19 @ 1:30 pm – 2:30 pm

Quantum Coherence and Dynamics Controlled by Light: 

From Higgs Bosons to Chiral Fermions

  Jigang Wang

Department of Physics & Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, IA 50011, USA

Revolutionary properties of quantum materials are often manifestations of coherence and entanglement, e.g. it exists between the Cooper pairs in high-temperature superconductors (SCs); it protects chiral charge transport from disorder scattering in topological states of matter (TSM). The recent development of ultrafast and terahertz (THz) spectroscopy tools facilitates discovering and understanding driven coherent systems involving SCs and TSM controllable by light. In this talk, I will discuss strategic advantages, with help of some recent examples, of implementing this approach to probe and control many-body quantum phases and collective modes by light-driven coherence, e.g., light-induced gapless superconductivity and high harmonics generation [1], forbidden Anderson pseudo-spin precessions [2], hidden gapless quantum fluid [3], hybrid Higgs modes [4], spin exciton modes [5], phonon-controlled topology switching [6, 7] and chiral charge pumping [8]…. We argue that the light-driven coherence and sub-cycle dynamic symmetry breaking demonstrated in these work revealed represent universal principles for emergent materials discovery and light-matter quantum control for quantum information science.

[1]  X. Yang, et al., Nature Photonics. 13, 707 (2019)

[2] C. Vaswani et al., Phys. Rev. Lett. arXiv:1912.01676 (2020)

[3] X. Yang, et al., Nature Materials. 17, 586 (2018).

[4] C. Vaswani, et al., submitted (2020)

[5] X. Yang, et al., Phys. Rev. Lett. 121, 267001 (2018)

[6] C. Vaswani, et al., Phys Rev X 10, 021013 (2020).

[7] X. Yang, et al., npj Quantum Materials 5, 13 (2020).

[8] L. Luo et al., submitted (2020)

Jun
26
Fri
Liang Jiang (The University of Chicago)
Jun 26 @ 1:30 pm – 2:30 pm
Title: Robust Quantum information Processing with Bosonic Modes

Abstract: Bosonic modes are widely used for quantum communication and information processing. Recent developments in superconducting circuits enable us to control bosonic microwave cavity modes and implement arbitrary operations allowed by quantum mechanics, such as quantum error correction against excitation loss errors. We investigate various bosonic codes, error correction schemes, and potential applications.
Sep
11
Fri
Adarsh Ganesan (NIST)
Sep 11 @ 1:30 pm – 2:30 pm

Phononic Frequency Combs – A New Addition to Photonics, MEMS,
Quantum Information Science, Molecular Science & Material Science

Phononic frequency combs (PFC) are the mechanical analogs of
celebrated photonic frequency combs. These represent a newly
documented physical phenomenon in the domain of vibrations [1]. The
emergence of PFC is mediated by the nonlinear coupling among phonon
modes. Through a series of experiments with mechanical resonators, the
fundamentals of PFC have been established. Phononic frequency combs
could find applications in photonics, quantum information science,
molecular science and material science. My talk will describe my
fundamental work on phononic frequency combs and my plan for future
research.

[1] Ganesan, A., Do, C. and Seshia, A., 2017. Phononic frequency comb
via intrinsic three-wave mixing. Physical review letters, 118(3),
p.033903.

Host: Phil

Sep
18
Fri
Berthold Jäck (Princeton/HKUST) **note the special time**
Sep 18 @ 10:00 am – 11:00 am

Observation of a Majorana zero mode in a topologically protected edge state

Superconducting pairing in the helical edge state of topological insulators is predicted to provide a unique platform for realizing Majorana zero modes (MZMs). We use (spin-polarized) scanning tunneling microscopy measurements to probe the influence of proximity induced superconductivity and local magnetism on the helical edge states of bismuth(111) thin films, which are grown on a superconducting niobium substrate and decorated with iron clusters. Consistent with model calculations, our measurements reveal the emergence of a localized MZM at the interface between the superconducting helical edge state and the ferromagnetic iron clusters with strong magnetization component along the edge (1). Our experiments also resolve the MZM’s unique spin signature by which it can be distinguished from trivial in-gap states that may accidently occur at zero energy in a superconductor. High-resolution spectroscopic mapping of quasiparticle interference further demonstrates quasiparticle backscattering inside the one-dimensional helical edge state, which is induced by the ferromagnetic iron clusters that locally break time-reversal symmetry (2).

(1)       B. Jäck, Y. Xie, J. Li, S. Jeon, B.A. Bernevig, A. Yazdani, Science 364, 1255-1259 (2019)

(2)       B. Jäck, Y. Xie, B.A. Bernevig, A. Yazdani, PNAS, DOI:10.1073/pnas.2005071117 (2020)

Host: Jen

Link to Zoom recording

Sep
25
Fri
Shubhayu Chatterjee (Berkeley)
Sep 25 @ 1:30 pm – 2:30 pm

Superconductivity from skyrmion condensation in magic angle graphene 

We propose and analyze a strong-coupling route to superconductivity in twisted bilayer graphene near the magic angle (MATBG). Starting from a promising ordered insulating state featuring Chern bands, we show that topological textures/skyrmions of the order parameter carry electric charge due to band topology. Subsequently, we find a natural all-electronic mechanism of attraction between two such charge e textures. This leads to pairing into charge 2e bosons, whose condensation can trigger superconductivity on doping away from the insulating state. We discuss microscopic aspects of this scenario, including energetics and an estimate of the effective mass which yields Tc for the superconductor, within the framework of an effective field theory. We back up our analytical calculations by large-scale DMRG numerics on a related model that captures the relevant symmetry and topology of the flat bands in MATBG. In DMRG, we find clear evidence for superconductivity driven by the binding of electrons into charge-2e skyrmions, even when Coulomb repulsion is by far the largest energy scale.

Host: Jen

Link to Zoom recording

Oct
2
Fri
Dmitry Pikulin (Microsoft Station Q)
Oct 2 @ 1:30 pm – 2:30 pm

Three-dimensional flat bands from inhomogeneous nodal-line semimetals

In this talk I will discuss the effects of inhomogeneous strain or chemical composition on the nodal line semimetals (NLSM). I will start by showing that quite generically inhomogeneity leads to Landau-level-like behavior in crystalline systems. NLSM as a Dirac system has zeroth Landau level which will be massively degenerate in a 3D system, forming a 3D approximately flat band. I will show the connection of such a flat band to the drumhead surface state of NLSM. I will apply this to models of realistic materials and will show that interactions may lead to formation of a superconducting or magnetic state stabilized by the geometric contribution to the superfluid stiffness.

Host: Jen

Link to Zoom recording

Oct
9
Fri
Gabriel Jose Goulart Cardoso (Stony Brook)
Oct 9 @ 1:30 pm – 2:30 pm
The boundary density profile of a Coulomb droplet: Freezing at the edge
We revisit the problem of computing the boundary density profile of a droplet of two-dimensional one-component plasma (2D OCP) with logarithmic interaction between particles in a confining harmonic potential. At a sufficiently low temperature but still in the liquid phase, the density exhibits oscillations as a function of the distance to the boundary of the droplet. We obtain the density profile numerically using Monte-Carlo simulations of the 2D OCP. We argue that the decay and period of those oscillations can be explained within a picture of the Wigner crystallization near the boundary, where the crystal is gradually melted with the increasing distance to the boundary.

Host: Sasha
Oct
16
Fri
Alexander Wietek (Flatiron Institute)
Oct 16 @ 1:30 pm – 2:30 pm

Stripes, Antiferromagnetism, and the Pseudogap in the Doped Hubbard Model at Finite Temperature

Host: Cyrus Dreyer

The phase diagram of the two-dimensional Hubbard model at finite temperature poses one of the most interesting conundrums in contemporary condensed matter physics. Tensor network techniques, such as matrix-product based approaches as well as 2D tensor networks, yield state-of-the-art unbiased simulations of the 2D Hubbard model at zero temperature and are capable of giving unbiased results at finite temperature as well. A promising approach for applying tensor networks to study finite-temperature quantum systems is the minimally entangled typical thermal state (METTS) algorithm, which is a Monte Carlo technique that samples from a family of entangled wavefunctions, and which offers favorable scaling and parallelism. In this talk I will present some of our recent results applying this technique in the strong coupling, low-temperature and finite hole-doping regime [1]. We discover that a novel phase characterized by commensurate short-range antiferromagnetic correlations and no charge ordering occurs at temperatures above the half-filled stripe phase extending to zero temperature. We find the single-particle gap to be smallest close to the nodal point and detect a maximum in the magnetic susceptibility. These features bear a strong resemblance to the pseudogap phase of high-temperature cuprate superconductors. The simulations are verified using a variety of different unbiased numerical methods in the three limiting cases of zero temperature, small lattice sizes, and half-filling.

[1] https://arxiv.org/abs/2009.10736

Link to Zoom recording