Dynamic conductivity scaling in photoexcitedV2O3thin films

Abstract

Optical-pump terahertz-probe spectroscopy is used to investigate ultrafast far-infrared conductivity dynamics during the insulator-to-metal transition (IMT) in vanadium sesquioxide (V 2 O 3 ).The resultant conductivity increase occurs on a tens of ps timescale, exhibiting a strong dependence on the initial temperature and fluence. We have identified a scaling of the conductivity dynamics upon renormalizing the time axis with a simple power law (α 1/2) that depends solely on the initial, final, and conductivity onset temperatures. Qualitative and quantitative considerations indicate that the dynamics arise from nucleation and growth of the metallic phase which can be described by the Avrami model. We show that the temporal scaling arises from spatial scaling of the growth of the metallic volume fraction, highlighting the self-similar nature of the dynamics.Our results illustrate the important role played by mesoscopic effects in phase transition dynamics. 1The variety of electronic, magnetic and structural phases exhibited by transition metal oxides arise from a delicate balance between competing degrees-of-freedom whose contribution to the macroscopic properties is challenging to ascertain [1]. An increasingly successful approach to this problem is that of time resolved experiments, where ultrafast excitation and probing enables the determination of fundamental material timescales down to femtosecond resolution [2][3][4]. Access to specific energy scales is made possible by ultrafast sources ranging from terahertz (THz) to x-ray frequencies. Initial all-optical measurements of electron-phonon relaxation in metals [5,6] have paved the way to time resolved investigations of complex systems, from spins in magnetic materials [7][8][9][10][11] to superconducting gaps [12,13] or to surface charges in topological insulators [14].To date, most time-resolved experiments in transition metal oxides, and in particular vanadates, have focused on microscopic dynamics [15][16][17][18][19][20][21][22]. For example, fast sub-ps electronic and structural responses have been reported for vanadium dioxide [15-17, 19, 21, 22].However, static measurements increasingly demonstrate that nano-to-meso scale phase coexistence is crucial in determining the properties of complex materials, including cuprates, manganites, and vanadates [23][24][25][26][27]. This naturally extends to dynamic investigations of the phase coexistence stage, as done in VO 2 [19,22,28,29]. At a minimum, neglecting mesoscale effects can lead to a misinterpretation of the dynamics. More importantly, as shown in this work, mesoscale dynamics are of intrinsic interest from fundamental and applied perspectives.V 2 O 3 is a paramagnetic metal with rhombohedral crystal symmetry [30][31][32][33][34][35] which undergoes a first order phase transition to an antiferromagnetic insulating state at T IM T = 175K, accompanied by a change to a monoclinic crystal structure [36]. In this work, we present mesoscopic conductivity dynamics of V 2 O 3 across the insulator-to-me...

Domain-size effects on the dynamics of a charge density wave in 1T−TaS2

“…However, the correlation length stays larger than during the growth. We suggest that the large domains and the domains with defects are more stable and therefore the intensity drop is mostly due to the disappearance of the small domains, which are less stable [26,27].…”

Origin of the current-driven breakdown in vanadium oxides: Thermal versus electronic

“…In Fig 2c, we compare the effective breakdown electric field with the square root of the breakdown fluence [24] in an independently measured optically driven V 2 O 3 transition. The two normalized curves agree, suggesting that the field dependence of the current driven V 2 O 3 transition is similar to the optically-driven transition.…”

Phase transition in bulk single crystals and thin films ofVO2by nanoscale infrared spectroscopy and imaging

“…Previously studied VO 2 nano-beams and micro-crystals can be regarded as specific cases with some of the unique strain environments identified in the present study [23][24][25]76]. In future studies, ultrafast femtosecond dynamics [77][78][79] and magnetic orders [1] can also be included in systematic near-field investigations of TMOs, which will lead to a better understanding of the rich diversity of mesoscopic and microscopic phenomena at fundamental time and length scales in materials such as manganites and high temperature superconductors. …”