Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L45: Electronic Correlations in di-chalcogenides and Related |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Rico Schoenemann, Natl High Magnetic Field Lab Room: LACC 505 |
Wednesday, March 7, 2018 11:15AM - 11:27AM |
L45.00001: Quantum phase transition in few layer NbSe2 probed through quantized conductance fluctuations Hemanta Kundu, Sujay Ray, Kapildeb Dolui, Vivas Bagwe, Palash Choudhury, S Krupanidhi, Tanmoy Das, Pratap Raychaudhuri, Aveek Bid We present the first experimental observations of a quantum phase transition (QPT) between two distinct charge density wave (CDW) phases in 2-dimensional 2H-NbSe2. Our studies were performed on suspended, ultra-thin 2H-NbSe2 devices fabricated on piezoelectric substrates. We establish, through sensitive conductance fluctuation spectroscopy, that on varying the strain the system undergoes a QPT between the familiar triangular 3Q CDW phase and a novel linear 1Q CDW phase. With the help of mean-field calculations, these observations can be explained as to arise from dynamical phase transition between the two CDW states. To affirm this idea, we vary the lateral strain across the device via piezoelectric medium and map out the phase diagram near the quantum critical point (QCP). The results resolve a long-standing mystery of the anomalously large spectroscopic gap in the density of states of 2H-NbSe2 measured through tunneling spectroscopy. |
Wednesday, March 7, 2018 11:27AM - 11:39AM |
L45.00002: Strain Engineering of a Charge Density Wave in a Transition Metal Dichalcogenide 2H-NbSe2 Shang Gao, Felix Flicker, R. Sankar, He Zhao, Zheng Ren, BRYAN RACHMILOWITZ, Sidhika Balachandar, Fangchang Chou, Kenneth Burch, Ziqiang Wang, Jasper Van Wezel, Ilija Zeljkovic Transition metal dichalcogenides host a range of fascinating optoelectronic properties. One of the prominent members of this family is the superconducting 2H-NbSe2 (Tc~7.2 K), which also hosts a charge density wave (CDW) phase (Tc~33 K) that has been intensely studied for decades. External perturbations, such as strain or pressure, can in principle push a CDW phase into a different ordering geometry. However, engineering this type of quantum criticality has been experimentally challenging. Here, we apply a new method in combination with STM/STS to deform and study the surface of 2H-NbSe2. We discuss the intriguing observation of two new CDW phases, which we can directly attribute to local strain. We combine our STS measurements of the electronic band structure with theoretical calculations to discover distinct roles of electrons and phonons in the formation of different phases. Our work establishes a new platform for the explorations of strain induced quantum phase transitions in this and other related materials. |
Wednesday, March 7, 2018 11:39AM - 11:51AM |
L45.00003: The condensation of electrons and holes in 2D photocells of ultrathin MoTe2 Trevor Arp, Dennis Pleskot, Vivek Aji, Nathaniel Gabor In semiconductors, electrons and holes above a certain critical density may condense into a liquid phase containing a macroscopic population of highly correlated electrons and holes. Strikingly, under optical excitation, ultrathin MoTe2 photocells undergo this transition even at room temperature (295 K). Using a new technique called Multi-Parameter Dynamic Photoresponse Microscopy (MPDPM) we image the photoresponse of two-dimensional graphene-MoTe2-graphene photocells over several dynamical variables, including laser power, pump-probe delay and applied voltage. MPDPM reveals that above a critical threshold a ring-like spatial feature abruptly forms in the photoresponse as a function of increasing optical power. This pattern, combined with time-resolved photocurrent dynamics also revealed by MPDPM, provides strong evidence for the formation of an electron-hole condensate at room temperature. |
Wednesday, March 7, 2018 11:51AM - 12:03PM |
L45.00004: Effect of electronic correlations in the electronic structure of MoTe2 Niraj Aryal, Efstratios Manousakis MoTe2 has been recently predicted to be a type-II Weyl material by DFT calculations and ARPES experiments seem to agree with the DFT predictions. However, quantum oscillation experiments (QOE) disagree with the DFT calculations; the most noteworthy discrepancy is the absence of large hole pocket in the QOE which is predicted to form a Weyl point with the electron pocket by the DFT calculations. This raises doubt about the existence of Weyl physics in this material. In an attempt to understand and resolve the discrepancy between the QOE and the DFT calculations and ARPES measurements, we investigated the role of electronic correlations within the GGA+U and GW approximations. |
Wednesday, March 7, 2018 12:03PM - 12:15PM |
L45.00005: Charge density wave order in monolayer metal dichalcogenides studied with scanning tunneling micriscopy Aidi Zhao, Huan Shan, Yahui Mao, Bing Wang Monolayer metal dichalcogenides, including TiSe2, NbSe2, SnSe2, as well as lateral heterojunctions of monolayer TiSe2/NbSe2, are synthesized with molecular beam epitaxy and characterized with low-temperature scanning tunneling microscopy and spectroscopy. These materials are particularly interesting due to the emergence of complex electronic orders at low temperatures, e.g. charge density wave (CDW) and superconductivity, even at the 2D limit. Here we report that seamless high-quality lateral heterojunctions can be grown between the 2D monolayer NbSe2 and TiSe2 by molecular beam epitaxy. Scanning tunneling microscopy reveals that the monolayer NbSe2 and TiSe2 in the heterostructure remains the (3×3×3) and (2×2×2) charge-density-wave orders of their bulk counterparts respectively at low temperature, leading to a first example of lateral CDW heterojunctions. More strikingly, we observe an unexpectedly unidirectional CDW proximity effect at the NbSe2 vicinity of the heterojunctions, implying a complicate interplay between the two CDW orders. |
Wednesday, March 7, 2018 12:15PM - 12:27PM |
L45.00006: A combination of ARPES and Neutron Scattering studies of the Jahn-Teller physics in 1T- TiSe2 Utpal Chatterjee, Despina Louca, Aaron Wegner, Junjing Zhao We have conducted temperature-dependent Angle Resolved Photoemission Spectroscopy (ARPES) and Neutron Scattering (NS) studies of 1T- TiSe2, a canonical commensurate Charge Density Wave (CDW) system. Our NS data provide evidences for Jahn-Teller (JT) distortions in 1T- TiSe2 both below and above the CDW transition temperature (Tcdw). In this context, JT distortion has been proposed to be one of the possible mechanisms of the CDW order in 1T- TiSe2. In one of the models relating the CDW order to JT distortion, proposed by Whangbo and Canadell (J. Am. Chem. Soc.,114, 9587-9600, 1992), the energy lowering in the CDW state occurs due to a downward movement of the Se 4p bands with decreasing temperature through Tcdw. Furthermore, there should be some shortening in Ti-Se bond-length in the observed displacement pattern at temperatures below Tcdw. These features are observed in our ARPES and Neutron Scattering studies. Being consistent with previous works, our ARPES data indeed show that both Ti 3d bands and Se 4p bands shift downward in energy as temperature of the material is reduced through Tcdw. However, the energy movement of Ti 3d bands is entirely due to the T-dependent change in chemical potential, while Se 4p bands do display nontrivial T-dependent motion. |
Wednesday, March 7, 2018 12:27PM - 12:39PM |
L45.00007: Exciton condensation temperature in a transition metal dichacogenide 1T-TiSe2. Jin Mo Bok, Han-Yong Choi We revisit the question of the transition metal dichacogenide TiSe2 charge density wave (CDW) state being an excitonic insulator. The BCS-like CDW gap equation with the inter and intra-band Coulomb interactions was employed to calculate the transition temperature as a function of the band gap. Realistic dispersions for one hole band centered at Γ and three electron bands at M points were considered to model the 1T-TiSe2. We discuss possibility of the 1T-TiSe2 CDW state originating from exciton condensation through the calculated phase diagram. |
Wednesday, March 7, 2018 12:39PM - 12:51PM |
L45.00008: Abstract Withdrawn
|
Wednesday, March 7, 2018 12:51PM - 1:03PM |
L45.00009: Energy dependent spatial texturing in the CDW of 1T-CuxTiSe2 Marcello Spera, Alessandro Scarfato, Enrico Giannini, Christoph Renner The competition between ground states is a central topic in modern condensed matter physics. It is of common belief that unconventional superconductivity (SC) emerges from a precursor state, which is suppressed upon the appearance of the superconducting condensate. |
Wednesday, March 7, 2018 1:03PM - 1:15PM |
L45.00010: Abstract Withdrawn
|
Wednesday, March 7, 2018 1:15PM - 1:27PM |
L45.00011: Sodium salt-assisted edge structure control of atomically thin monolayers of transition metal dichalcogenides Xufan Li, Ethan Kahn, Kazunori Fujisawa, Tianyi Zhang, Mauricio Terrones, Avetik Harutyunyan The growth of large-sized, highly crystalline two-dimensional (2D) monocrystals with controllable edge structures is highly desired when exploring novel properties and optimize/control functionalities. The use of different precursors during chemical vapor deposition (CVD) facilitates the growth of 2D crystals by assisting the reaction or by modifying surface properties of the substrates. In this work, we used sodium halides (i.e., NaBr, NaCl) in CVD growth of MoS2 monolayers when reacting MoO2 and S. We successfully synthesized MoS2 monolayer single crystals with lateral sizes up to 250 µm and controlled edge morphology (curved or straight). These different morphologies exhibited characteristic edge structures consisting of Mo- or S-terminated zigzag edges. These edge structures were studied by aberration corrected high-resolution scanning transmission electron microscopy (AC-HRSTEM). In this presentation, we will discuss the role of sodium halides in the presence of MoO2 and S; as well as the role of substrates. This salt-assisted growth has shown to be an effective method for rationally controlling the size and morphology of 2D MoS2 single crystals, and allows edge termination manipulation at the atomic level, which is crucial for tailoring the properties and applications. |
Wednesday, March 7, 2018 1:27PM - 1:39PM |
L45.00012: Polaronic transport and thermoelectricity in Fe1-xCoxSb2S4 (x = 0, 0.1, and 0.2) Yu Liu, Chang-Jong Kang, Eli Stavitski, Qianheng Du, Klaus Attenkofer, Gabriel Kotliar, Cedomir Petrovic Correlated electron materials such as FeSb2 possess the highest thermoelectric power factor in nature and thermoelectric power up to 45 mV K-1. We present a study of Co-doped magnetic semiconductor Fe1-xCoxSb2S4 (x = 0, 0.1, and 0.2), which crystallize in an orthorhombic structure with Pnma space group, similar to FeSb2. In contrast to Fe1-xCoxSb2 and Fe1-xCrxSb2 where electronic transport is dominated by thermal activation and variable range hopping, our results indicate polaronic transport due to the large discrepancy between activation energy for conductivity, Eρ (146 ~ 270 meV), and thermopower, ES (47 ~ 108 meV), in Fe1-xCoxSb2S4. Bulk magnetization and heat capacity measurements of FeSb2S4 show a broad antiferromagnetic transition (TN = 46 K) followed by an additional weak transition (T* = 50 K). The TN and T* slightly decrease with increase in x. This is also reflected in thermal conductivity measurement, indicating strong spin-lattice coupling. Fe1-xCoxSb2S4 shows high value of thermopower (up to ~ 624 μV K-1 at 300 K) and significantly smaller thermal conductivity, a feature desired for potential applications based on FeSb2 materials. |
Wednesday, March 7, 2018 1:39PM - 1:51PM |
L45.00013: Antiferroelectric Distortion with Anomalous Phonon Softening in Excitonic Insulator Ta2NiSe5 Akitoshi Nakano, Shinya Tamura, Naoyuki Katayama, Takumi Hasegawa, Satoshi Tsutsui, Hiroshi Sawa Ta2NiSe5 is proposed as a candidate substance for excitonic insulator (E.I.) because the top of the valence band is anomalous flattened below the transition temperature as shown by photoemission spectroscopy measurements (Ts =328 K)[1]. The E.I. transition of Ta2NiSe5 is accompanied with orthorhombic to monoclinic structural phase transition at Ts [2]. The theoretical calculation predicted that the transition is driven by exciton condensation which makes a particular phonon mode at q~0 instable[3]. However, the appropriate phonon soft mode has not been observed yet.To identify the phonon mode which plays a major role for the structural phase transition, we carried out a synchrotron inelastic X-ray scattering and diffraction experiments. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700