Atomic lattice disorder in charge-density-wave phases of exfoliated dichalcogenides (1T-TaS2)

Charge-density waves (CDWs) and their concomitant periodic lattice distortions (PLDs) govern the electronic properties in several layered transition-metal dichalcogenides. In particular, 1T-TaS2 undergoes a metal-to-insulator phase transition as the PLD becomes commensurate with the crystal lattice. Here we directly image PLDs of the nearly commensurate (NC) and commensurate (C) phases in thin, exfoliated 1T-TaS2 using atomic resolution scanning transmission electron microscopy at room and cryogenic temperature. At low temperatures, we observe commensurate PLD superstructures, suggesting ordering of the CDWs both in- and out-of-plane. In addition, we discover stacking transitions in the atomic lattice that occur via one-bond-length shifts. Interestingly, the NC PLDs exist inside both the stacking domains and their boundaries. Transitions in stacking order are expected to create fractional shifts in the CDW between layers and may be another route to manipulate electronic phases in layered dichalcogenides.

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Satellite Dark Field Microscopy of Charge Density Wave Domains in Transition-Metal Dichalcogenides

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600001434 ◽

1980 ◽

Vol 38 ◽

pp. 338-339

Author(s):

K. K. Fung ◽

J. W. Steeds

Keyword(s):

Transition Metal ◽

Charge Density ◽

Density Wave ◽

Transition Metal Dichalcogenides ◽

Dark Field ◽

Charge Density Waves ◽

Periodic Lattice ◽

Dark Field Microscopy ◽

Metal Dichalcogenides ◽

Lattice Distortions

Transition-metal dichalcogenides are layer compounds which exhibit anomalies in their transport properties at low temperatures. Diffraction studies have shown that the anomalies are associated with the formation of charge density waves (CDW) coupled to periodic lattice distortions (1). This is manifested as satellite spots decorating Bragg reflections. The satellite spots can be used to image the structure associated with the CDW transitions in dark field. This is accomplished by tilting the specimen so that a satellite spot is strongly excited. In this way, we have imaged domains in the incommensurate and commensurate states of transition-metal dichalcogenides. The existence of CDW domains has been predicted theoretically (2). Using a commercial single-tilting hot stage and a liquid-helium-cooled double-tilting stage built in this laboratory in a Philips EM400 microscope we have studied the nature of domains in several IT polytype transition-metal dichalcogenides between 40K and 600K.

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Structure and control of charge density waves in two-dimensional 1T-TaS2

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1512092112 ◽

2015 ◽

Vol 112 (49) ◽

pp. 15054-15059 ◽

Cited By ~ 109

Author(s):

Adam W. Tsen ◽

Robert Hovden ◽

Dennis Wang ◽

Young Duck Kim ◽

Junichi Okamoto ◽

...

Keyword(s):

Charge Density ◽

Hexagonal Boron Nitride ◽

Density Wave ◽

Transition Metal Dichalcogenides ◽

Inert Atmosphere ◽

Charge Density Waves ◽

Melting Transition ◽

Assembly Method ◽

Metal Dichalcogenides ◽

Layered Transition Metal

The layered transition metal dichalcogenides host a rich collection of charge density wave phases in which both the conduction electrons and the atomic structure display translational symmetry breaking. Manipulating these complex states by purely electronic methods has been a long-sought scientific and technological goal. Here, we show how this can be achieved in 1T-TaS2 in the 2D limit. We first demonstrate that the intrinsic properties of atomically thin flakes are preserved by encapsulation with hexagonal boron nitride in inert atmosphere. We use this facile assembly method together with transmission electron microscopy and transport measurements to probe the nature of the 2D state and show that its conductance is dominated by discommensurations. The discommensuration structure can be precisely tuned in few-layer samples by an in-plane electric current, allowing continuous electrical control over the discommensuration-melting transition in 2D.

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Thermal properties of layered transition-metal dichalcogenides at charge-density-wave transitions

Physical Review B ◽

10.1103/physrevb.15.2943 ◽

1977 ◽

Vol 15 (6) ◽

pp. 2943-2951 ◽

Cited By ~ 101

Author(s):

J. M. E. Harper ◽

T. H. Geballe ◽

F. J. DiSalvo

Keyword(s):

Thermal Properties ◽

Transition Metal ◽

Charge Density ◽

Charge Density Wave ◽

Density Wave ◽

Transition Metal Dichalcogenides ◽

Metal Dichalcogenides ◽

Layered Transition Metal

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Epitaxial Growth and Charge Density Wave of TaSe2

MRS Proceedings ◽

10.1557/proc-230-231 ◽

1991 ◽

Vol 230 ◽

Cited By ~ 1

Author(s):

Toshihiro Shimada ◽

Fumio S. Ohuchi ◽

Bruce A. Parkinson

Keyword(s):

Transition Metal ◽

Charge Density ◽

Epitaxial Growth ◽

Ultrathin Films ◽

Charge Density Wave ◽

Density Wave ◽

Transition Metal Dichalcogenides ◽

Charge Density Waves ◽

Density Waves ◽

Metal Dichalcogenides

AbstractWe report an epitaxial growth of TaSe2, a family of transition metal dichalcogenides that exhibit Charge Density Waves (CDW). The films that have been characterized with RHEED, LEED, XPS and STM showed two different phases. Occurrence of CDW in the ultrathin films has been detected by XPS and LEED.

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