Temperature and electric field tuning of the ferroelectric soft mode in a strainedSrTiO3/DyScO3heterostructure

Abstract

We studied THz dielectric spectra of SrTiO 3 / DyScO 3 epitaxial multilayers with four 50-nm-thick layers of each compound deposited on DyScO 3 substrate as a function of temperature and electric field. At room temperature, SrTiO 3 is in the paraelectric phase and, due to the in-plane tensile strain within the films, the soft-mode frequency is shifted down to 47 cm −1 . The ferroelectric phase transition occurs in the strained SrTiO 3 layers around 270 K and in the ferroelectric phase the soft-mode hardening upon temperature decrease is observed. The soft mode is linearly coupled to an excitation of relaxation type at 10 cm −1 at all temperatures. This relaxation is silent in the paraelectric phase, but it becomes coupled to the polarization below the ferroelectric transition temperature and its strength progressively increases. The recently proposed universal model of soft-mode behavior in strained SrTiO 3 films ͓C. Kadlec et al., J. Phys.: Condens. Matter 21, 115902 ͑2009͔͒ was generalized to describe the observed spectra at all temperatures and applied fields.

Influence of the central mode and soft phonon on the microwave dielectric loss near the strain-induced ferroelectric phase transitions inSrn+1TiGoian1, Kamba2, Orloff3 et al. 2014Phys. Rev. B13280View full textAdd to dashboardCite

“…In fact, 1% tensile strain can even induce the ferroelectricity near 270 K in 50-nm-thick SrTiO 3 thin films deposited on (110) DyScO 3 substrates [15]. The ε of such films can be significantly tuned by an applied electric field at kilohertz (kHz), MW [15], and terahertz (THz) [16] frequencies, because the soft mode (SM) frequency is sensitive to external electric field [16]. Nevertheless, MW dielectric loss of strained SrTiO 3 thin films at room temperature is comparable to Ba 1−x Sr x TiO 3 ceramics [15].…”

“…Nevertheless, MW dielectric loss of strained SrTiO 3 thin films at room temperature is comparable to Ba 1−x Sr x TiO 3 ceramics [15]. Kadlec et al [16] have attributed these losses to a central mode (i.e., dielectric relaxation below the phonon frequencies, abbreviation CM) that arises in the dielectric [18]). spectra of SrTiO 3 thin films as the material approaches temperatures close to the FE phase transition.…”

Terahertz Conductivity of Twisted Bilayer Graphene

“…2(a). Before BLG deposition, the substrates for sample and reference were carefully characterized by THz-TDStheir phase difference yields the thickness difference ∆L between the two substrates, which must be taken into account in our subsequent analysis [23]. After the main pulse, a weaker pulse (etalon) appears due to multiple reflections in the z-cut quartz substrate.…”

Strain-Induced Ferroelectricity of a SrTiO3 Thin Film on a MgAl2O4 Substrate Observed by Terahertz Time-Domain Spectroscopy

“…An increase in dielectric constant in a gigahertz frequency region have been observed with some perovskite-type ferroelectric materials, e.g. BiTiO 3 [15,16], (Bi, Sr)TiO 3 [17], and strained SrTiO 3 [10], and contributions of order-disorder type ferroelectric components and/or anharmonic soft mode potential are thought to be dominant. In our previous study, the STO/MgO thin film formed did not exhibit any ferroelectric properties and such an increase in ε″ at low frequencies was not observed [18].…”

“…Therefore, the lattice mismatch between STO and DSO(110) is +1.02%, which introduces in-plane tensile strain in a STO thin film on a DSO(110) substrate. Ever since the report on the study of ferroelectricity at room temperature was published, strained STO thin films have been extensively studied [5][6][7][8][9][10]. In particular, we expect that strained STO thin films can be used as functional components in terahertz photonic devices, which are now receiving increasing attention in various fields [11,12].…”