B. Gorshunov - Profile on Academia.edu (original) (raw)

Papers by B. Gorshunov

Coherent source submillimeter wave spectroscopy

Topics in Applied Physics

ABSTRACT

Polar Phonons and Specific Features of the Ferroelectric States in Cadmium Titanate

Physics of the Solid State, 2005

ABSTRACT

Temperature dependence of the optical properties of the organic superconductor (ET)2Cu(NCS)2 in the submillimeter range

Physica Status Solidi (a), 1989

Journal of Biological Physics, 2018

Employing optical spectroscopy we have performed a comparative study of the dielectric response o... more Employing optical spectroscopy we have performed a comparative study of the dielectric response of extracellular matrix and filaments of electrogenic bacteria Shewanella oneidensis MR-1, cytochrome c, and bovine serum albumin. Combining infrared transmission measurements on thin layers with data of the terahertz spectra, we obtain the dielectric permittivity and AC conductivity spectra of the materials in a broad frequency band from a few cm −1 up to 7000 cm −1 in the temperature range from 5 to 300 K. Strong absorption bands are observed in the three materials that cover the range from 10 to 300 cm −1 and mainly determine the terahertz absorption. When cooled down to liquid helium temperatures, the bands in Shewanella oneidensis MR-1 and cytochrome c reveal a distinct fine structure. In all three materials, we identify the presence of liquid bound water in the form of librational and translational absorption bands at ≈ 200 and ≈ 600 cm −1 , respectively. The sharp excitations seen above 1000 cm −1 are assigned to intramolecular vibrations.

Far-infrared hopping conductivity in the CuO chains of a single-domain YBa 2 Cu 3 O 7 − δ crystal

Physical Review B, 1992

We report on the observation of far-infrared hopping conductivity in the CuO chains of a single-d... more We report on the observation of far-infrared hopping conductivity in the CuO chains of a single-domain YBa2Cu3O7-delta crystal. Our results suggest that at low temperatures the mean free path of carriers in the chains is mainly determined by scattering at oxygen vacancies, while at higher temperatures scattering at phonons occurs additionally.

Far-Infrared and Microwave Intragap Absorption in a YBa 2 Cu 3 O 7-δ Thin Film at Low Temperature

Europhysics Letters (EPL), 1991

ABSTRACT We report on a study of far-infrared and microwave intragap absorption of a YBa2Cu3O7-δ ... more ABSTRACT We report on a study of far-infrared and microwave intragap absorption of a YBa2Cu3O7-δ thin film at low temperature. Our results suggest a superconducting energy gap with 2Δ(0)/kBTc ≈ 7 and residual, intragap absorption for temperatures T Tc that consists of three portions, a microwave and a far-infrared band of possibly nonintrinsic nature and sharp phonon resonances of intrinsic nature.

Physical Review B, 2018

Transport, magnetic and optical investigations on EuRbFe 4 As 4 single crystals evidence that the... more Transport, magnetic and optical investigations on EuRbFe 4 As 4 single crystals evidence that the ferromagnetic ordering of the Eu 2+ magnetic moments at T N = 15 K, below the superconducting transition (Tc = 36 K), affects superconductivity in a weak but intriguing way. Upon cooling below T N , the zero resistance state is preserved and the superconductivity is affected by the in-plane ferromagnetism mainly at domain boundaries; a perfect diamagnetism is recovered at low temperatures. The infrared conductivity is strongly suppressed in the far-infrared region below Tc, associated with the opening of a complete superconducting gap at 2∆ = 10 meV. A gap smaller than the weak coupling limit suggests the strong orbital effects or, within a multiband superconductivity scenario, the existence of a larger yet unrevealed gap.

Physics Reports, 2006

The quasi-one-dimensional cuprates (La,Y,Sr,Ca) 14 Cu 24 O 41 , consisting of spin-chains and spi... more The quasi-one-dimensional cuprates (La,Y,Sr,Ca) 14 Cu 24 O 41 , consisting of spin-chains and spin-ladders, have attracted much attention, mainly because they represent the first superconducting copper oxide with a non-square lattice. Theoretically, in isolated hole-doped two-leg ladders, superconductivity is tightly associated with the spin gap, although in competition with a chargedensity wave (CDW). Indeed, both the gapped spin-liquid and CDW states have been established in the doped spin-ladders of Sr 14−x Ca x Cu 24 O 41 , however the relevance of these objects to electronic properties and superconductivity is still subject of intensive discussion. In this treatise, an appreciable set of experimental data is reviewed, which has been acquired in recent years, indicating a variety of magnetic and charge arrangements found in the chains and ladders of underdoped (La,Y) y (S,Ca) 14−y Cu 24 O 41 and fully doped Sr 14−x Ca x Cu 24 O 41. Based on these data, phase diagrams are constructed for the chains of underdoped systems (as a function of La, Y-substitution), as well as for the chains and ladders of the fully doped ones (as a function of Ca-substitution). We try to reconcile contradictory results concerning the charge dynamics in the ladders, like the hole redistribution between ladders and chains, collective modes and pseudogap, field-dependent transport and the temperature scales and doping levels at which the two-dimensional CDW develops in the ladder planes. The remaining open issues are clearly extracted. In the discussion the experimental results are contrasted with theoretical predictions, which allows us to conclude with two important remarks concerning the nature of the competing CDW and superconducting ground states. A density wave in ladders, characterized by a sinusoidal charge modulation, belongs to the class of broken symmetry patterns, which is theoretically predicted for strongly correlated lowdimensional electron systems; however its precise texture and nature is still an open issue. As for superconductivity, the presence of the spin gap in the normal state points towards d-wave symmetry and magnetic origin of the attractive interaction. However, there is a finite density of mobile quasi-particles that appears for high Ca contents and increases with pressure, concomitantly with increased two-dimensionality and metallicity. For this reason the superconductivity in the doped ladders of Sr 14−x Ca x Cu 24 O 41 which occurs under high pressure cannot simply be a stabilization of the d-wave superconductivity expected for a pure single ladder system.

Physical Review B, 2019

Using Fourier-transform infrared spectroscopy and optical ellipsometry, room temperature spectra ... more Using Fourier-transform infrared spectroscopy and optical ellipsometry, room temperature spectra of complex conductivity of single crystals of hexaborides GdxLa1−xB6, x(Gd)= 0, 0.01, 0.1, 0.78, 1 are determined in the frequency range 30-35000 cm −1. In all compounds, in addition to the Drude free-carrier spectral component, a broad excitation is discovered with the unusually large dielectric contribution ∆ε=5000-15000 and non-Lorentzian lineshape. It is suggested that the origin of the excitation is connected with the dynamic cooperative Jahn-Teller effect of B6 clusters. Analysis of the spectra together with the results of DC and Hall resistivity measurements shows that only 30-50% of the conduction band electrons are contributing to the free carrier conductivity with the rest being involved in the formation of an overdamped excitation, thus providing possible explanation of remarkably low work function of thermoemission of GdxLa1−xB6 and non-Fermi-liquid behavior in GdB6 crystals.

Physical Review B, 2000

The results of wide-range measurements of the low-frequency, rf, and microwave conductivity in th... more The results of wide-range measurements of the low-frequency, rf, and microwave conductivity in the typical mixed-valent narrow-gap semiconductor samarium hexaboride are presented. The established steplike anomaly of conductivity ͑͒ around 10 GHz is discussed in the framework of the exciton-polaron approach and coherent-state formation in SmB 6 at helium temperatures. A combined analysis of the dc-and wide-range ac-transport characteristics and dielectric permittivity data at low temperatures is developed.

2008 33rd International Conference on Infrared, Millimeter and Terahertz Waves, 2008

With an MBE technique, a Si/Ge heterostructures are prepared containing layers of nanostructured ... more With an MBE technique, a Si/Ge heterostructures are prepared containing layers of nanostructured Ge with quantum dots of size of several nanometers. The effective conductivity of the layers is determined by a quasioptical terahertz-subterahertz coherent source BWO spectroscopy. The conductivity is found to be strongly enhanced compared with the conductivity of bulk germanium. Possible microscopic mechanisms responsible for the enhancement will be discussed. Application of BWO spectrometers for obtaining precise quantitative information on of dielectric properties at THz-subTHz frequencies of semiconducting layers and structures is demonstrated by presenting the temperature dependences of dielectric characteristics of a commercial silicon wafer at frequencies 0.3 to 1.2 THz and temperatures 5 K-300 K.

Physical Review B, 2010

The low-energy electrodynamic response of a series of La 0.25 Ca 0.75 MnO 3 samples of different ... more The low-energy electrodynamic response of a series of La 0.25 Ca 0.75 MnO 3 samples of different morphology is systematically studied in the frequency range from 4 to 700 cm −1 ͑0.1-20 THz, quantum energies 0.4-90 meV͒ with particular attention focused at frequencies below 40 cm −1. In the antiferromagnetically ordered phase below 140 K, a resonancelike absorption band appears in the spectra around 20-40 cm −1 that is assigned to acoustical phonons which acquire optical activity due to a fourfold superstructure appearance in the crystallographic a direction and correspondent Brillouin-zone folding. Nanosize effects in charge and magnetic subsystems are investigated by measuring the spectra of samples with grain diameters reduced from several micrometers down to 40 nm. A strong relaxation in the lowest-frequency spectra is observed above 100 K in all samples, indicating that the charge-order transition shows characteristics typical for order-disorder transitions.

Phase Transitions, 2014

20 cm ¡1 (at 5 K) is observed with three rather narrow resonances at its high-frequency shoulder ... more 20 cm ¡1 (at 5 K) is observed with three rather narrow resonances at its high-frequency shoulder (38, 42 and 46 cm ¡1). The origin of these low-energy excitations is discussed.

We measured the terahertz (THz) complex conductivity of Ca doped YBa2Cu3O 7−δ thin films in the f... more We measured the terahertz (THz) complex conductivity of Ca doped YBa2Cu3O 7−δ thin films in the frequency range of 0.1 to 3 THz (3 to 100 cm −1) and at a temperature range of 20 to 300 K. The films were measured using both time domain and frequency domain THz methods. We showed evidence for the existence of a sub-gap in overdoped Y1−xCaxBa2Cu3O 7−δ samples doped with 5% and 10% Ca. Evidence for the opening of this sub-gap appears as a sharp decrease in the spectrum of the real part of conductivity at frequencies equivalent to a gap energy of 1 meV and is more prominent with increased doping. This decrease in conductivity can be explained by using d x 2 −y 2-wave pairing symmetry with an imaginary part of is or idxy which suggests node removal.

Physical Review B, 2003

We show that the spin chain/ladder compound La3Sr3Ca8Cu24O41 is an insulator with hopping transpo... more We show that the spin chain/ladder compound La3Sr3Ca8Cu24O41 is an insulator with hopping transport along the chains. In the temperature range 35-280 K, DC conductivity σDC(T) follows Mott's law of variable-range hopping conduction; the frequency dependence has the form σ(ν, T) = σDC(T)+A(T)•ν s , where s ≈ 1. The conduction mechanism changes from variable-range hopping to nearest-neighbor hopping around Tc = 300 K. The chain array thus behaves like a one-dimensional disordered system. Disorder is due to random structural distortions of chains induced by irregular coordination of the La/Sr/Ca ions.

Physical Review B, 2001

Thorough Raman and infrared ͑IR͒ reflectivity investigations of nominally pure SrTiO 3 ceramics i... more Thorough Raman and infrared ͑IR͒ reflectivity investigations of nominally pure SrTiO 3 ceramics in the 10-300 K range have revealed a clear presence of the polar phase whose manifestation steeply increases on cooling. The Raman strengths of the Raman-forbidden IR modes are proportional to TO1 Ϫ␣ (␣Ϸ1.6) where TO1 is the polar soft mode frequency. No pronounced permittivity dispersion is observed below the soft mode frequency so that, as in single crystals, the static permittivity is essentially determined by the soft mode contribution. A theory is suggested which assumes a frozen dipole moment connected with the grain boundaries which induces the polar phase in the grain bulk in correlation with the bulk soft-mode frequency. This stiffens slightly the effective soft mode response and reduces the low-temperature permittivity compared to that of single crystals. Moreover, the polar soft mode strongly couples to the E g component of the structural soft doublet showing that the polar axis is perpendicular to the tetragonal axis below the structural transition which is shifted to 132 K in our ceramics. Whereas the TiO 6 octahedra tilt ͑primary order parameter͒ below the structural transition corresponds to that in single crystals, much smaller A 1g-E g splitting of the structural soft doublet shows that the tetragonal deformation ͑secondary order parameter͒ is nearly 10 times smaller, apparently due to the grain volume clamping in ceramics.

Technical Physics, 2008

IR spectra of metal-containing diamondlike silicon-carbon films are taken for the first time. It ... more IR spectra of metal-containing diamondlike silicon-carbon films are taken for the first time. It is shown that the optical response from the subsystem of free charge carriers in chromium-containing films can be described in terms of a simple model that deals with carriers localized inside clusters several nanometers in size. The data obtained indicate that the electric and dielectric properties of the films can be controlled by technological means during their synthesis and by varying the size, concentration, and conductivity of metallic nanoclusters.

Infrared reflectance of anisotropic (110) YBCO epitaxial film

Solid State Communications, 1989

ABSTRACT

Electrodynamic properties of nanoporous silicon in the range from terahertz to infrared frequencies

Physics of the Solid State, 2007

ABSTRACT

Coherent source submillimeter wave spectroscopy

Topics in Applied Physics

ABSTRACT

Polar Phonons and Specific Features of the Ferroelectric States in Cadmium Titanate

Physics of the Solid State, 2005

ABSTRACT

Temperature dependence of the optical properties of the organic superconductor (ET)2Cu(NCS)2 in the submillimeter range

Physica Status Solidi (a), 1989

Journal of Biological Physics, 2018

Employing optical spectroscopy we have performed a comparative study of the dielectric response o... more Employing optical spectroscopy we have performed a comparative study of the dielectric response of extracellular matrix and filaments of electrogenic bacteria Shewanella oneidensis MR-1, cytochrome c, and bovine serum albumin. Combining infrared transmission measurements on thin layers with data of the terahertz spectra, we obtain the dielectric permittivity and AC conductivity spectra of the materials in a broad frequency band from a few cm −1 up to 7000 cm −1 in the temperature range from 5 to 300 K. Strong absorption bands are observed in the three materials that cover the range from 10 to 300 cm −1 and mainly determine the terahertz absorption. When cooled down to liquid helium temperatures, the bands in Shewanella oneidensis MR-1 and cytochrome c reveal a distinct fine structure. In all three materials, we identify the presence of liquid bound water in the form of librational and translational absorption bands at ≈ 200 and ≈ 600 cm −1 , respectively. The sharp excitations seen above 1000 cm −1 are assigned to intramolecular vibrations.

Far-infrared hopping conductivity in the CuO chains of a single-domain YBa 2 Cu 3 O 7 − δ crystal

Physical Review B, 1992

We report on the observation of far-infrared hopping conductivity in the CuO chains of a single-d... more We report on the observation of far-infrared hopping conductivity in the CuO chains of a single-domain YBa2Cu3O7-delta crystal. Our results suggest that at low temperatures the mean free path of carriers in the chains is mainly determined by scattering at oxygen vacancies, while at higher temperatures scattering at phonons occurs additionally.

Far-Infrared and Microwave Intragap Absorption in a YBa 2 Cu 3 O 7-δ Thin Film at Low Temperature

Europhysics Letters (EPL), 1991

ABSTRACT We report on a study of far-infrared and microwave intragap absorption of a YBa2Cu3O7-δ ... more ABSTRACT We report on a study of far-infrared and microwave intragap absorption of a YBa2Cu3O7-δ thin film at low temperature. Our results suggest a superconducting energy gap with 2Δ(0)/kBTc ≈ 7 and residual, intragap absorption for temperatures T Tc that consists of three portions, a microwave and a far-infrared band of possibly nonintrinsic nature and sharp phonon resonances of intrinsic nature.

Physical Review B, 2018

Transport, magnetic and optical investigations on EuRbFe 4 As 4 single crystals evidence that the... more Transport, magnetic and optical investigations on EuRbFe 4 As 4 single crystals evidence that the ferromagnetic ordering of the Eu 2+ magnetic moments at T N = 15 K, below the superconducting transition (Tc = 36 K), affects superconductivity in a weak but intriguing way. Upon cooling below T N , the zero resistance state is preserved and the superconductivity is affected by the in-plane ferromagnetism mainly at domain boundaries; a perfect diamagnetism is recovered at low temperatures. The infrared conductivity is strongly suppressed in the far-infrared region below Tc, associated with the opening of a complete superconducting gap at 2∆ = 10 meV. A gap smaller than the weak coupling limit suggests the strong orbital effects or, within a multiband superconductivity scenario, the existence of a larger yet unrevealed gap.

Physics Reports, 2006

The quasi-one-dimensional cuprates (La,Y,Sr,Ca) 14 Cu 24 O 41 , consisting of spin-chains and spi... more The quasi-one-dimensional cuprates (La,Y,Sr,Ca) 14 Cu 24 O 41 , consisting of spin-chains and spin-ladders, have attracted much attention, mainly because they represent the first superconducting copper oxide with a non-square lattice. Theoretically, in isolated hole-doped two-leg ladders, superconductivity is tightly associated with the spin gap, although in competition with a chargedensity wave (CDW). Indeed, both the gapped spin-liquid and CDW states have been established in the doped spin-ladders of Sr 14−x Ca x Cu 24 O 41 , however the relevance of these objects to electronic properties and superconductivity is still subject of intensive discussion. In this treatise, an appreciable set of experimental data is reviewed, which has been acquired in recent years, indicating a variety of magnetic and charge arrangements found in the chains and ladders of underdoped (La,Y) y (S,Ca) 14−y Cu 24 O 41 and fully doped Sr 14−x Ca x Cu 24 O 41. Based on these data, phase diagrams are constructed for the chains of underdoped systems (as a function of La, Y-substitution), as well as for the chains and ladders of the fully doped ones (as a function of Ca-substitution). We try to reconcile contradictory results concerning the charge dynamics in the ladders, like the hole redistribution between ladders and chains, collective modes and pseudogap, field-dependent transport and the temperature scales and doping levels at which the two-dimensional CDW develops in the ladder planes. The remaining open issues are clearly extracted. In the discussion the experimental results are contrasted with theoretical predictions, which allows us to conclude with two important remarks concerning the nature of the competing CDW and superconducting ground states. A density wave in ladders, characterized by a sinusoidal charge modulation, belongs to the class of broken symmetry patterns, which is theoretically predicted for strongly correlated lowdimensional electron systems; however its precise texture and nature is still an open issue. As for superconductivity, the presence of the spin gap in the normal state points towards d-wave symmetry and magnetic origin of the attractive interaction. However, there is a finite density of mobile quasi-particles that appears for high Ca contents and increases with pressure, concomitantly with increased two-dimensionality and metallicity. For this reason the superconductivity in the doped ladders of Sr 14−x Ca x Cu 24 O 41 which occurs under high pressure cannot simply be a stabilization of the d-wave superconductivity expected for a pure single ladder system.

Physical Review B, 2019

Using Fourier-transform infrared spectroscopy and optical ellipsometry, room temperature spectra ... more Using Fourier-transform infrared spectroscopy and optical ellipsometry, room temperature spectra of complex conductivity of single crystals of hexaborides GdxLa1−xB6, x(Gd)= 0, 0.01, 0.1, 0.78, 1 are determined in the frequency range 30-35000 cm −1. In all compounds, in addition to the Drude free-carrier spectral component, a broad excitation is discovered with the unusually large dielectric contribution ∆ε=5000-15000 and non-Lorentzian lineshape. It is suggested that the origin of the excitation is connected with the dynamic cooperative Jahn-Teller effect of B6 clusters. Analysis of the spectra together with the results of DC and Hall resistivity measurements shows that only 30-50% of the conduction band electrons are contributing to the free carrier conductivity with the rest being involved in the formation of an overdamped excitation, thus providing possible explanation of remarkably low work function of thermoemission of GdxLa1−xB6 and non-Fermi-liquid behavior in GdB6 crystals.

Physical Review B, 2000

The results of wide-range measurements of the low-frequency, rf, and microwave conductivity in th... more The results of wide-range measurements of the low-frequency, rf, and microwave conductivity in the typical mixed-valent narrow-gap semiconductor samarium hexaboride are presented. The established steplike anomaly of conductivity ͑͒ around 10 GHz is discussed in the framework of the exciton-polaron approach and coherent-state formation in SmB 6 at helium temperatures. A combined analysis of the dc-and wide-range ac-transport characteristics and dielectric permittivity data at low temperatures is developed.

2008 33rd International Conference on Infrared, Millimeter and Terahertz Waves, 2008

With an MBE technique, a Si/Ge heterostructures are prepared containing layers of nanostructured ... more With an MBE technique, a Si/Ge heterostructures are prepared containing layers of nanostructured Ge with quantum dots of size of several nanometers. The effective conductivity of the layers is determined by a quasioptical terahertz-subterahertz coherent source BWO spectroscopy. The conductivity is found to be strongly enhanced compared with the conductivity of bulk germanium. Possible microscopic mechanisms responsible for the enhancement will be discussed. Application of BWO spectrometers for obtaining precise quantitative information on of dielectric properties at THz-subTHz frequencies of semiconducting layers and structures is demonstrated by presenting the temperature dependences of dielectric characteristics of a commercial silicon wafer at frequencies 0.3 to 1.2 THz and temperatures 5 K-300 K.

Physical Review B, 2010

The low-energy electrodynamic response of a series of La 0.25 Ca 0.75 MnO 3 samples of different ... more The low-energy electrodynamic response of a series of La 0.25 Ca 0.75 MnO 3 samples of different morphology is systematically studied in the frequency range from 4 to 700 cm −1 ͑0.1-20 THz, quantum energies 0.4-90 meV͒ with particular attention focused at frequencies below 40 cm −1. In the antiferromagnetically ordered phase below 140 K, a resonancelike absorption band appears in the spectra around 20-40 cm −1 that is assigned to acoustical phonons which acquire optical activity due to a fourfold superstructure appearance in the crystallographic a direction and correspondent Brillouin-zone folding. Nanosize effects in charge and magnetic subsystems are investigated by measuring the spectra of samples with grain diameters reduced from several micrometers down to 40 nm. A strong relaxation in the lowest-frequency spectra is observed above 100 K in all samples, indicating that the charge-order transition shows characteristics typical for order-disorder transitions.

Phase Transitions, 2014

20 cm ¡1 (at 5 K) is observed with three rather narrow resonances at its high-frequency shoulder ... more 20 cm ¡1 (at 5 K) is observed with three rather narrow resonances at its high-frequency shoulder (38, 42 and 46 cm ¡1). The origin of these low-energy excitations is discussed.

We measured the terahertz (THz) complex conductivity of Ca doped YBa2Cu3O 7−δ thin films in the f... more We measured the terahertz (THz) complex conductivity of Ca doped YBa2Cu3O 7−δ thin films in the frequency range of 0.1 to 3 THz (3 to 100 cm −1) and at a temperature range of 20 to 300 K. The films were measured using both time domain and frequency domain THz methods. We showed evidence for the existence of a sub-gap in overdoped Y1−xCaxBa2Cu3O 7−δ samples doped with 5% and 10% Ca. Evidence for the opening of this sub-gap appears as a sharp decrease in the spectrum of the real part of conductivity at frequencies equivalent to a gap energy of 1 meV and is more prominent with increased doping. This decrease in conductivity can be explained by using d x 2 −y 2-wave pairing symmetry with an imaginary part of is or idxy which suggests node removal.

Physical Review B, 2003

We show that the spin chain/ladder compound La3Sr3Ca8Cu24O41 is an insulator with hopping transpo... more We show that the spin chain/ladder compound La3Sr3Ca8Cu24O41 is an insulator with hopping transport along the chains. In the temperature range 35-280 K, DC conductivity σDC(T) follows Mott's law of variable-range hopping conduction; the frequency dependence has the form σ(ν, T) = σDC(T)+A(T)•ν s , where s ≈ 1. The conduction mechanism changes from variable-range hopping to nearest-neighbor hopping around Tc = 300 K. The chain array thus behaves like a one-dimensional disordered system. Disorder is due to random structural distortions of chains induced by irregular coordination of the La/Sr/Ca ions.

Physical Review B, 2001

Thorough Raman and infrared ͑IR͒ reflectivity investigations of nominally pure SrTiO 3 ceramics i... more Thorough Raman and infrared ͑IR͒ reflectivity investigations of nominally pure SrTiO 3 ceramics in the 10-300 K range have revealed a clear presence of the polar phase whose manifestation steeply increases on cooling. The Raman strengths of the Raman-forbidden IR modes are proportional to TO1 Ϫ␣ (␣Ϸ1.6) where TO1 is the polar soft mode frequency. No pronounced permittivity dispersion is observed below the soft mode frequency so that, as in single crystals, the static permittivity is essentially determined by the soft mode contribution. A theory is suggested which assumes a frozen dipole moment connected with the grain boundaries which induces the polar phase in the grain bulk in correlation with the bulk soft-mode frequency. This stiffens slightly the effective soft mode response and reduces the low-temperature permittivity compared to that of single crystals. Moreover, the polar soft mode strongly couples to the E g component of the structural soft doublet showing that the polar axis is perpendicular to the tetragonal axis below the structural transition which is shifted to 132 K in our ceramics. Whereas the TiO 6 octahedra tilt ͑primary order parameter͒ below the structural transition corresponds to that in single crystals, much smaller A 1g-E g splitting of the structural soft doublet shows that the tetragonal deformation ͑secondary order parameter͒ is nearly 10 times smaller, apparently due to the grain volume clamping in ceramics.

Technical Physics, 2008

IR spectra of metal-containing diamondlike silicon-carbon films are taken for the first time. It ... more IR spectra of metal-containing diamondlike silicon-carbon films are taken for the first time. It is shown that the optical response from the subsystem of free charge carriers in chromium-containing films can be described in terms of a simple model that deals with carriers localized inside clusters several nanometers in size. The data obtained indicate that the electric and dielectric properties of the films can be controlled by technological means during their synthesis and by varying the size, concentration, and conductivity of metallic nanoclusters.

Infrared reflectance of anisotropic (110) YBCO epitaxial film

Solid State Communications, 1989

ABSTRACT

Electrodynamic properties of nanoporous silicon in the range from terahertz to infrared frequencies

Physics of the Solid State, 2007

ABSTRACT