Femtometer atomic displacement, the root cause for multiferroic behavior of CuO unearthed through polarized Raman spectroscopy

Abstract

Recently, CuO has been proposed as a potential multiferroic material with high transition temperature. Competing models based on spin current and ionic displacements are invoked to explain ferroelectricity in CuO. The theoretical model based on ionic displacement predicted very small displacement (∼10−5 Å) along the b axis. Experimentally detecting displacements of such a small amplitude in a particular direction is extremely challenging. Through our detailed angle resolved polarized Raman spectroscopy study on single crystal of CuO, we have validated the theoretical study and provided direct evidence of displacement along the b axis. Our study provides important contribution in the high temperature multiferroic compounds and showed for the first time, the use of the polarized Raman scattering in detecting ionic displacements at the femtometer scale.

Tracing microscopic atomic displacements using polarized Raman spectroscopy: a case study on BaTiO3

“…The main advantage of this method is its ability to track extremely small atomic displacements which is very difficult by using conventional techniques as mentioned in introduction section. Up to now, we have successfully detected small displacement in highly insulator NdGaO 3 [12] and the atomic displacement of ∼10 −5 Å in multiferroic CuO [11] and we expect even better resolution by improving the signal to noise ratio. In literature, as per our knowledge, only two attempts had been made to detect the atomic displacements at such small length scale.…”

“…So, equation (1) can be written as ∆ω Ti = K cc ε cc for tetragonal phase. (11) Similarly, in orthorhombic and rhombohedral phase Ti ion displaces along (101) pc and (111) pc directions, respectively. Therefore,…”

“…Here, we claim that the polarized Raman spectroscopy (PRS) can be used to extract information about the extremely small atomic rearrangements in the crystalline solids due to presence of the external perturbations like temperature, light photon, electric and magnetic field. Earlier, we have successfully used this method in measuring femto-meter scale atomic displacements in CuO [11] and NdGaO 3 [12] single crystals across ferroelectric and structural transition temperature, respectively. To check the accuracy and reliability of the method, in this report, we have performed PRS study on classical ferroelctric material BaTiO 3 (BTO) as a case study to detect atomic displacement and the obtained results are compared with the well-established experimental and theoretical results.…”

“…Specific Raman tensor element can be traced in PRS using proper polarization configuration. Therefore, Raman intensity collected in the two polarization configurations (parallel and cross) in various crystallographic directions should reflect the change associated with the atomic rearrangements, if any, along the different crystallographic directions [11,12]. In other words, any kind of atomic rearrangements or change in inter atomic distances in a single crystal can be tracked using PRS by choosing proper polarization configuration.…”

Resolving Vibrations in a Polyatomic Molecule with Femtometer Precision

“…So far, the smallest spatially resolved vibrational feature has been measured at 0.6 pm [39]. A quantification of structural changes on the fewfemtometer level [40][41][42][43] and potentially below [44,45] has been thus far limited to solid-state systems.…”