Bias-Voltage Driven Switching of the Charge-Density-Wave and Normal Metallic Phases in 1T-TaS₂ Thin-Film Devices

Abstract

We report on switching among three charge-density-wave phases -commensurate, nearly commensurate, incommensurate -and the high-temperature normal metallic phase in thin-film 1T-TaS2 devices induced by application of an in-plane electric field. The electric switching among all phases has been achieved over a wide temperature range, from 77 K to 400 K. The low-frequency electronic noise spectroscopy has been used as an effective tool for monitoring the transitions, particularly the switching from the incommensurate charge-density-wave phase to the normal metal phase. The noise spectral density exhibits sharp increases at the phase transition points, which correspond to the step-like changes in resistivity. Assignment of the phases is consistent with low-field resistivity measurements over the temperature range from 77 K to 600 K. Analysis of the experimental data and calculations of heat dissipation suggest that Joule heating plays a dominant role in the electric-field induced transitions in the tested 1T-TaS2 devices on Si/SiO2 substrates. The possibility of electrical switching among four different phases of 1T-TaS2 is a promising step toward nanoscale device applications. The results also demonstrate the potential of noise spectroscopy for investigating and identifying phase transitions in materials. Keywords: charge-density-wave effects; van der Waals materials; resistive switching, lowfrequency noise, 1T-TaS2; normal metallic phase Electric Switching of the Charge-Density-Wave and Normal Metallic Phases in 1T-TaS2 Thin-Film Devices -UC Riverside 2019 3 | P a g eSwitching between various material phases at room temperature by the application of electric field has the potential of becoming a new device paradigm for future electronic and optoelectronic technologies 1-4 . Among the promising material candidates, which must exhibit phase changes characterized by abrupt resistivity changes and hysteresis, is the 1T polymorph of tantalum disulfide (TaS2). The quasi-two-dimensional (2D) van der Waals layered crystalline 1T-TaS2 exhibits charge-density-wave (CDW) effects, i.e. periodic modulation of the charge density and the underlying lattice resulting from the interplay between the electron-electron and electronphonon interactions [5][6][7][8][9][10][11][12][13]14 . The CDW state becomes fully commensurate with the lattice below ~200 K 15-17 . The commensurate CDW (C-CDW) consists of a √13 × √13 reconstruction within the basal plane that forms a star-of-David pattern in which each star contains 13 Ta atoms. The Fermi surface, composed of 1 d-electron per star, is unstable, so that the lattice reconstruction is accompanied by a Mott-Hubbard transition that fully gaps the Fermi surface and increases the resistance 15,18-21 . As the temperature increases above 180 K, the C-CDW phase breaks up into a nearly commensurate CDW (NC-CDW) phase that consists of ordered C-CDW regions separated by domain walls 22 . This C-CDW to NC-CDW transition is revealed as an abrupt change in the resistance with a large hysteresis window i...

A time-domain phase diagram of metastable states in a charge ordered quantum material

“…We see that the H state has a nearly temperature-independent threshold uence and is stable at low temperature in agreement with Ref. 3. When the measurement timescale is longer than the relaxation time, the H state disappears, thus the C/H boundary moves to lower temperature with time.…”

“…Such states are typically formed through phase transitions under non-equilibrium conditions and the nal state is reached through processes that span a large range of timescales. By using time-resolved optical techniques and femtosecond-pulse-excited scanning tunneling microscopy (STM), the evolution of the metastable states in the quasi-two-dimensional dichalcogenide 1T-TaS 2 is mapped out on a temporal phase diagram using the photon density and temperature as control parameters on timescales ranging from to s. The introduction of a time-domain axis in the phase diagram enables us to follow the evolution of metastable emergent states created by different phase transition mechanisms on different timescales, thus enabling comparison with theoretical predictions of the phase diagram and opening the way to understanding of the complex ordering processes in metastable materials.Short optical or electrical pulses can create non-equilibrium conditions that lead to electronic self-organization in quantum materials which can be usefully applied in various devices [1][2][3][4][5][6][7][8][9] . Recent rapid progress in the timedomain investigations of non-equilibrium phase transitions has led to the observation of a variety of emergent transient and metastable states in complex quantum materials, including organic electronic crystals 10 , oxides 11,12 , dichalcogenides 13 , and fullerene superconductors 14 .…”

Electron-phonon interactions and two-phonon modes associated with charge density wave in single crystalline 1T−VSe2

“…Most 2D materials exist in two stable crystal structures such as 2H (trigonal prismatic) and 1T (octahedron), where the physical properties depend on the symmetry of the phases [13]. Among the several versatile properties, the CDW is a novel phenomenon realized in 1T and 2H polytypes of many metallic layered TMDCs, such as NbSe 2 , TaSe 2 , TaS 2 , VTe 2 , and VSe 2 [14][15][16][17][18][19][20]. Thus, these materials have received much scientific and technological attention for many-body interactions and potential applications in memory devices, transistors, logic-gate electronics, and oscillators [14][15][16][17][18][19][20].…”

“…Among the several versatile properties, the CDW is a novel phenomenon realized in 1T and 2H polytypes of many metallic layered TMDCs, such as NbSe 2 , TaSe 2 , TaS 2 , VTe 2 , and VSe 2 [14][15][16][17][18][19][20]. Thus, these materials have received much scientific and technological attention for many-body interactions and potential applications in memory devices, transistors, logic-gate electronics, and oscillators [14][15][16][17][18][19][20]. The origin of the CDW in TMDCs has not achieved any general scientific consensus and has remained a topic of investigation so far [5,[21][22][23][24].…”

A time-domain phase diagram of metastable states in a charge ordered quantum material

“…hort optical or electrical pulses can create non-equilibrium conditions that lead to electronic self-organization in quantum materials which can be usefully applied in various devices [1][2][3][4][5][6][7][8][9] . Recent rapid progress in the time-domain investigations of non-equilibrium phase transitions has led to the observation of a variety of emergent transient and metastable states in complex quantum materials, including organic electronic crystals 10 , oxides 11,12 , dichalcogenides 13 , and fullerene superconductors 14 .…”