Microwave sources with high stability and low phase noise are required for radar and satellite co... more Microwave sources with high stability and low phase noise are required for radar and satellite communication systems. Many solid — state sources for such applications employ crystal oscillators in the 100 MHz range followed by frequency multiplier chains. Increasingly sophisticated modern microwave communication systems, require more efficient, more reliable and smaller sources.
Low phase noise local oscillators are essential components in a microwave system. In order to pro... more Low phase noise local oscillators are essential components in a microwave system. In order to provide a low noise stable oscillator utilising microwave integrated circuit technique the necessity for the provision of a high Q resonator structure arises.
The problem of the shielding current distribution in the partially "resistive" HTS film is numeri... more The problem of the shielding current distribution in the partially "resistive" HTS film is numerically investigated for the time-harmonic magnetic field created by a small fiat coil. As an alternative, a simple model based solution of the problem is also given. The results are used for contactless determination of the electrical characteristics of YBCO films on different substrates at 77 K.
We report a range of experiments designed to test the efficacy of spin polarized injection from c... more We report a range of experiments designed to test the efficacy of spin polarized injection from colossal magnetoresistive material (CMR) into high temperature superconductors (HTS). These include traditional transport measurements, studies of CMR/YBCO contacts, measurements of penetration depth and studies of the effect of spin-injection on the critical state of square thin films and rings. We have used pulsed currents to minimize heating and have made comparisons with the non-magnetic homologue of CMR LaNiO3. Our experiments provide evidence that there is a measurable effect, but that it is small and mainly confined to 10 20 nm of the YBCO surface. Current gain of about 0.2 has been observed.
ABSTRACT The complex differential susceptibility of a YBCO film and YBCO–STO–LCMO structures with... more ABSTRACT The complex differential susceptibility of a YBCO film and YBCO–STO–LCMO structures with different thicknesses of the STO layer (0, 2, and 7 nm) is investigated. It is shown that for a YBCO–LCMO structure the temperature of the superconducting transition Tonset and the critical current density jc are observed to decrease in comparison with a pure YBCO film. In a YBCO–STO–LCMO structure, on the contrary, Tonset increases, while jc increases for the structure with the 2 nm thickness of STO and decreases for that with 7 nm of STO. It is conjectured that there is a change of the vortex pinning mechanism as the temperature is lowered.
We report measurements of the /f noise in 75 nm, 100 nm and 200 nm thick La0.7Sr0.3MnO3 (LSMO) th... more We report measurements of the /f noise in 75 nm, 100 nm and 200 nm thick La0.7Sr0.3MnO3 (LSMO) thin films deposited onto (100) SrTiO3 substrates by pulsed laser deposition. The samples were patterned using photolithography into bridges with various widths (20 mum to 150 mum) and lengths (50 mum to 300 mum). The voltage noise spectra Sv(f) clearly showed two regions: excess noise depending on the bias current with a 1/f behavior at low frequency and Johnson noise (4kTR where R is the resistance of the device) at higher frequency. In the investigated 10 Hz - 100 kHz frequency range no deviation from the 1/f behavior was noticed neither as a function of the temperature (300 - 400 K) nor of the bias current. We particularly investigated the validity of the semi-empirical Hooge relation in the 300 - 400 K temperature range, which means across the metal-insulator transition. The voltage noise density SV in LSMO bridges was found to be proportional to the square of the bias voltage V in th...
... Library Welcome Message Help Library Welcome Message Help. close. Attention, institutional on... more ... Library Welcome Message Help Library Welcome Message Help. close. Attention, institutional online journal administrators: if the institution name printed in this screen message is incorrect, you can request a change by sending an email to [email protected]. ...
The effects of planar hole concentration, p, and magnetic field on the resistivity, ρ(T), of high... more The effects of planar hole concentration, p, and magnetic field on the resistivity, ρ(T), of high-quality c-axis oriented crystalline thin films and sintered Y 1-x Ca x Ba 2 (Cu 1-y Zn y ) 3 O 7-δ samples were investigated over a wide range of Ca, Zn, and oxygen contents. Zn was used to suppress superconductivity and this enabled us to extract the characteristic pseudogap temperature, T
Microwave sources with high stability and low phase noise are required for radar and satellite co... more Microwave sources with high stability and low phase noise are required for radar and satellite communication systems. Many solid — state sources for such applications employ crystal oscillators in the 100 MHz range followed by frequency multiplier chains. Increasingly sophisticated modern microwave communication systems, require more efficient, more reliable and smaller sources.
Low phase noise local oscillators are essential components in a microwave system. In order to pro... more Low phase noise local oscillators are essential components in a microwave system. In order to provide a low noise stable oscillator utilising microwave integrated circuit technique the necessity for the provision of a high Q resonator structure arises.
The problem of the shielding current distribution in the partially "resistive" HTS film is numeri... more The problem of the shielding current distribution in the partially "resistive" HTS film is numerically investigated for the time-harmonic magnetic field created by a small fiat coil. As an alternative, a simple model based solution of the problem is also given. The results are used for contactless determination of the electrical characteristics of YBCO films on different substrates at 77 K.
We report a range of experiments designed to test the efficacy of spin polarized injection from c... more We report a range of experiments designed to test the efficacy of spin polarized injection from colossal magnetoresistive material (CMR) into high temperature superconductors (HTS). These include traditional transport measurements, studies of CMR/YBCO contacts, measurements of penetration depth and studies of the effect of spin-injection on the critical state of square thin films and rings. We have used pulsed currents to minimize heating and have made comparisons with the non-magnetic homologue of CMR LaNiO3. Our experiments provide evidence that there is a measurable effect, but that it is small and mainly confined to 10 20 nm of the YBCO surface. Current gain of about 0.2 has been observed.
ABSTRACT The complex differential susceptibility of a YBCO film and YBCO–STO–LCMO structures with... more ABSTRACT The complex differential susceptibility of a YBCO film and YBCO–STO–LCMO structures with different thicknesses of the STO layer (0, 2, and 7 nm) is investigated. It is shown that for a YBCO–LCMO structure the temperature of the superconducting transition Tonset and the critical current density jc are observed to decrease in comparison with a pure YBCO film. In a YBCO–STO–LCMO structure, on the contrary, Tonset increases, while jc increases for the structure with the 2 nm thickness of STO and decreases for that with 7 nm of STO. It is conjectured that there is a change of the vortex pinning mechanism as the temperature is lowered.
We report measurements of the /f noise in 75 nm, 100 nm and 200 nm thick La0.7Sr0.3MnO3 (LSMO) th... more We report measurements of the /f noise in 75 nm, 100 nm and 200 nm thick La0.7Sr0.3MnO3 (LSMO) thin films deposited onto (100) SrTiO3 substrates by pulsed laser deposition. The samples were patterned using photolithography into bridges with various widths (20 mum to 150 mum) and lengths (50 mum to 300 mum). The voltage noise spectra Sv(f) clearly showed two regions: excess noise depending on the bias current with a 1/f behavior at low frequency and Johnson noise (4kTR where R is the resistance of the device) at higher frequency. In the investigated 10 Hz - 100 kHz frequency range no deviation from the 1/f behavior was noticed neither as a function of the temperature (300 - 400 K) nor of the bias current. We particularly investigated the validity of the semi-empirical Hooge relation in the 300 - 400 K temperature range, which means across the metal-insulator transition. The voltage noise density SV in LSMO bridges was found to be proportional to the square of the bias voltage V in th...
... Library Welcome Message Help Library Welcome Message Help. close. Attention, institutional on... more ... Library Welcome Message Help Library Welcome Message Help. close. Attention, institutional online journal administrators: if the institution name printed in this screen message is incorrect, you can request a change by sending an email to [email protected]. ...
The effects of planar hole concentration, p, and magnetic field on the resistivity, ρ(T), of high... more The effects of planar hole concentration, p, and magnetic field on the resistivity, ρ(T), of high-quality c-axis oriented crystalline thin films and sintered Y 1-x Ca x Ba 2 (Cu 1-y Zn y ) 3 O 7-δ samples were investigated over a wide range of Ca, Zn, and oxygen contents. Zn was used to suppress superconductivity and this enabled us to extract the characteristic pseudogap temperature, T
Uploads
Papers by R. Chakalov