A simple method for the Kramers-Kronig analysis of reflectance spectra measured with diamond anvil cell

Okamura, Hidekazu

doi:10.1088/1742-6596/359/1/012013

Cited by 13 publications

(13 citation statements)

References 20 publications

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“…3(a) were obtained from R 0 (ω) using the conventional KK analysis, 29,30 while those at high pressure in Figs. 3(b)-3(d) were obtained from R d (ω) using a modified KK analysis, which took into account the refractive index of diamond as previously discussed in detail. 40 At P =0 and T =200 K, in Fig. 3(a), σ(ω) is almost flat above 500 cm −1 , and rises rapidly with decreasing frequency.…”

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confidence: 92%

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

et al. 2013

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Optical reflectance R(ω) of a pressure-induced superconductor SrFe2As2 has been measured under external pressure to 6 GPa and at temperatures to 8 K. Optical conductivity σ(ω) has been derived from the measured R(ω). At ambient pressure, in the antiferromagnetic state below TN=198 K, a pronounced feature develops in σ(ω) due to the opening of a spin density wave (SDW) gap, as already reported in the literature. With increasing pressure, the SDW gap feature in σ(ω) is progressively suppressed. At 4 GPa, where the sample is superconducting, the SDW gap feature in σ(ω) is strongly reduced than that at ambient pressure, but is still clearly observed. At 6 GPa, the SDW gap is completely suppressed. The pressure evolutions of the SDW gap magnitude and the spectral weight closely follow the pressure evolution of TN. PACS numbers:Regarding the superconductivity (SC) exhibited by Fe-based compounds, 1 the pressure-induced SC exhibited by the stoichiometric "122" compounds AFe 2 As 2 (A=Ba, Ca, Sr, Eu) have attracted much interest. 2-13 They exhibit SC with external pressure only, although many other families of Fe based superconductors require some form of chemical doping or deviation from stoichiometry to exhibit SC. 1 In particular, SrFe 2 As 2 (Sr122) and BaFe 2 As 2 (Ba122) show pressure-induced SC at relatively high temperatures of T c =34 K 5,7-9 and 28 K, 4,7,9,11 , respectively. Interestingly, the 122 compounds also show SC with chemical doping, as shown by (Sr, K)Fe 2 As 2 , 14 Sr(Fe,Co) 2 As 2 , 15 and SrFe 2 (As, P) 2 . 16 At ambient pressure, the stoichiometric 122 compounds are antiferromagnetic (AFM), poor metals. For Sr122 and Ba122, the AFM transition temperature (T N ) is 198 K and 136 K, respectively. At T N , the resistivity [ρ(T )] shows a kink and rapid decrease with cooling below T N . With increasing pressure, T N is gradually lowered, and the kink in ρ(T ) becomes broadened. Above a critical pressure, the SC appears. Similar suppression of AFM and emergence of SC have also been observed with chemical doping. [14][15][16] In this regard, both methods have provided a lot of insight, but one advantage of the pressure technique compared with chemical doping is that the former does not cause disorder in the crystal lattice.However, there is an additional complication regarding the pressure-induced SC in the 122 compounds. Namely, it has been shown that the pressure evolutions of the AFM and SC states strongly depend on the hydrostaticity. 8,11,12 Here, hydrostaticity refers to how isotropic the pressure acting on the sample is. The hydrostaticity in a high pressure experiment depends on the types of pressure cell and pressure transmitting medium used. Figure 1 summarizes the results of high pressure studies on Sr122. 4,5,7-9 As discussed in detail later, these results show that the AFM state is suppressed and SC appears at lower pressure when the applied pressure is less hydrostatic (more uniaxial). This may indicate that a uniaxial stress promotes SC in the 122 compounds.To probe the microscopic elect...

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confidence: 92%

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

et al. 2013

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“…As one measures the sample reflectivity within a DAC, one has to modify the method of analysis in order to account for the sample/diamond interface and also to compensate the renormalisation made against the spectrum of the gasket instead of a gold mirror. As was already pointed out by several studies, [26][27][28][29] it is possible to perform a Kramers-Kronig (KK) analysis based on the calculated reflectance at the sample/diamond interface…”

Section: Discussionmentioning

confidence: 99%

Versatile setup for optical spectroscopy under high pressure and low temperature

Tran

Levallois

Akrap

et al. 2015

Review of Scientific Instruments

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We present an optical setup for spectroscopic measurements in the infrared and of Raman shift under high pressure and at low temperature. Using a membrane-driven diamond anvil cell, the pressure can be tuned in situ up to 20 GPa and the temperatures ranges from room temperature down to 18 K in transmission mode and 13 K in reflection mode. In transmission, the setup is entirely working under vacuum to reduce the water absorption features and obtain a higher spectral stability. Since the infrared throughput obtained with a thermal source is limited, the use of a synchrotron source allowed to enhance the performance, as illustrated with results obtained with various materials. The analysis of the reflectivity is adapted so that it benefits from ambient pressure data and produces quantitative optical conductivity curves that can be easily compared to the results at ambient pressure.

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“…The high sensitivity ATR detection is realised with multi-reflection slabs/prisms where the number of reflections from the sample-prism interface can increase more than ten times [24]. Amplitude and phase changes for such a situation becomes cumulative and reflection (for E-field) can be expressed as [25]:r…”

Section: Four-polarisation (4-pol) Methods For Atrmentioning

confidence: 99%

Attenuated Total Reflection at THz Wavelengths: Peculiarities of Total Internal Reflection and Polariscopy

Ryu¹,

Ng²,

Anand³

et al. 2021

Preprint

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Capabilities of the Attenuated Total Reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials is presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1-0.5 mm depth due to strong refractive index change &sim;0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with possibility of frustrated total internal reflection (a breakdown of the ATR reflection-mode into transmission-mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling was used to model behaviour of absorber-scatterer inside materials at the interface with ATR prism for realistic complex refractive indices of bio-materials. Modality of ATR with polarisation analysis is proposed and its principle illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is revealed. Design principles of polarisation active optical elements and spectral filters are outlined. The results and concepts are based on experiments carried out at the THz beamline of the Australian Synchrotron.

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A simple method for the Kramers-Kronig analysis of reflectance spectra measured with diamond anvil cell

Cited by 13 publications

References 20 publications

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

Versatile setup for optical spectroscopy under high pressure and low temperature

Attenuated Total Reflection at THz Wavelengths: Peculiarities of Total Internal Reflection and Polariscopy

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A simple method for the Kramers-Kronig analysis of reflectance spectra measured with diamond anvil cell

Cited by 13 publications

References 20 publications

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe2As2

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe2As2

Versatile setup for optical spectroscopy under high pressure and low temperature

Attenuated Total Reflection at THz Wavelengths: Peculiarities of Total Internal Reflection and Polariscopy

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Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂