Thermoelectric power, also known as the Seebeck coefficient (S), is a vital property for under- standing electronic transport in materials. It provides insights into the energy dependence of the density of states near the Fermi surface , as well as the effects of electron-phonon and electron-magnon interactions. Additionally, it indicates the nature of charge carriers in a material and plays a key role in assessing thermoelectric efficiency for practical applications.

The efficiency of thermoelectric materials is commonly characterized by the dimensionless figure of merit (ZT ). In recent years, thermoelectric research has gained momentum due to increasing global energy demands, environmental concerns, and the need for sustainable energy solutions. Converting waste heat into useful electrical energy requires materials with high ZT , necessitating efficient, low-cost, and rapid experimental methods for screening potential materials. Several experimental setups for measuring thermoelectric power (TEP) in bulk materials and thin films have been developed. These techniques include scanning probe methods, integrated heater-sensor systems, and differential or two-thermocouple techniques. Each method has specific strengths and limitations, and most allow for TEP measurements as a function of temperature with or without magnetic fields.

The DSC setup, illustrated in Fig. 2, utilizes two nearly identical PT-100 resistors as substrates. These substrates are strategically positioned on top of a temperature-regulated copper block acting as a thermal bath. A glass coverslip, serving as a poor thermal conductor, separates the substrates from the thermal bath. The sample under investigation is affixed to sensor 1 while sensor 2 functions as a reference. During transitions, such as the absorption or release of latent heat, the temperature of substrate A (T1) diverges from that of the reference substrate 2. The transition temperature and latent heat can be deduced from the temperature difference between the two substrates (T1−T2), with T2 also utilized for temperature measurement. The copper block, acting as the thermal bath, serves as a stable heat source or reservoir due to its significantly larger heat capacity compared to both the sample and substrate capacities. Temperature control is facilitated by a Lakeshore 332 temperature controller, aided by a cartridge heater and an additional PT-100 thermometer mounted on the thermal reservoir.

This calorimeter unit is compact, designed for seamless integration into most conventional cryostats. The experiments utilized an Oxford Instrument’s liquid helium flow cryostat, occasionally augmenting cooling efficiency with static exchange gas. Achieving a nearly perfect linear temperature ramp from 100 K to 300 K, at maximum scan rates approximately upto 20 K/min, was feasible through proper selection of proportional, integral, and derivative (PID) values within the temperature controller. The experimental setup, illustrated in Fig.2, includes an electrical circuit featuring a balanced bridge network integrated with these two PT-100 sensors. An SR 830 lock-in amplifier, combined with an SRS 554 preamplifier, was utilized to bias the bridge network and measure the balance voltage response with high precision. During abrupt phase transitions, such as the absorption or release of latent heat by substrate 1, observable changes occur in the relative temperatures between substrates 1 and 2.

Terahertz Time-Domain Spectroscopy (THz-TDS) is a cutting-edge technique that employs ultrafast laser pulses to both generate and sample broadband THz radiation. By capturing measurements in both space and time, the THz pulse can be reconstructed with high precision. Advances in femtosecond laser technology have greatly enhanced the versatility and effectiveness of THz spectroscopy setups, making them well-suited for probing quantum materials directly. The unique properties of THz radiation, including its non-ionizing nature, non-invasive approach, phase-sensitive coherent detection, and significant penetration capability, make it a powerful tool in experimental condensed matter research.

Temperature Control Process:

1. Measurement: The temperature of the tube furnace was measured using a thermocouple (Type JK).

2. Signal Processing: The analog signal from the thermocouple was sent to the analog pin of the Arduino UNO via a thermocouple-to-digital converter module MAX 6675, allowing the system to read the temperature value.

3. Comparison: Once the temperature value was received, the microcontroller compared it to the set temperature.

4. Output Control: If the set temperature was higher than the measured value, the Arduino UNO sent a digital output signal via the Pulse Width Modulation (PWM) pin. This signal was sent to a Solid-State Relay (SSR), which controlled the power line connected to the furnace. The relay was activated when the PWM pin provided voltage, thus powering the furnace heating element.

5. Temperature Stabilization: To stabilize the furnace temperature, a proportional-integral-derivative (PID) control algorithm was implemented.

The entire automation system was integrated with LabVIEW software, allowing precise temperature control, with the system capable of stabilizing the furnace temperature up to 700°C.