Yhyjyk

I don't know why there is so much space between the section's title and the beginning of the text. I am using the same 'template' for others documents and it works normally.

 documentclass[twocolumn,prl,nobalancelastpage,aps,10pt] revtex4-1
 %documentclass[rmp,preprint]revtex4-1
usepackage[latin9]inputenc
usepackage[english]babel
usepackagegraphicx,bm,times
usepackagesubfig
graphicspath C:/Varie/UNI/MANO/primosemestre/fraboni/esperimenti/RT/pictures/ 
begindocument

titleElectrical resistance of Cu, Ni and Ge in the range $120K$ - $400K$

author...

affiliation...

beginabstract 
We observed the temperature dependence of the electrical resistance of Cu, Ni and Ge in the range between $200K$ and $400K$. It resulted to be linear in the whole range for Cu and Ni. The one of the Ge exhibited this linear behaviour only up to $300K$ showing an exponential decay above. We also estimated the energy gap $E_g$ of Ge which resulted to be equal to $E_g=$
endabstract

datetoday

maketitle
sectionINTRODUCTION
The aim of this study is to observe the dependence of the electrical resistance of two metals, Copper and Nickel, and of a doped semiconductor, the Germanium, as a function of the temperature. Furthermore our measurements allowed us to estimate the energy gap of the Germanium.
 %The two metals showed a linear dependence while the semiconductor has two different behaviour. Through our measuments 
 \

 The starting point of our discussion are ... 

Let us first have a look on the corrected mwe of you to recreate the issue. Please see that I deleted some packages not needed for this issue and please see that package times is outdated. To get the issue I used your The starting point of our discussion are ... some more times, because with blindtext I can not define the needed lines to show your issue.

I marked with <========= the relevant code:

documentclass[twocolumn,prl,nobalancelastpage,aps,10pt] revtex4-1
 %documentclass[rmp,preprint]revtex4-1
usepackage[latin9]inputenc
usepackage[english]babel
usepackagetimes % <======================================== outdated!

usepackageblindtext % <============================ to add dummy text


begindocument

titleElectrical resistance of Cu, Ni and Ge in the range $120K$ - $400K$

author...

affiliation...

beginabstract 
We observed the temperature dependence of the electrical resistance of Cu, Ni and Ge in the range between $200K$ and $400K$. It resulted to be linear in the whole range for Cu and Ni. The one of the Ge exhibited this linear behaviour only up to $300K$ showing an exponential decay above. We also estimated the energy gap $E_g$ of Ge which resulted to be equal to $E_g=$
endabstract

datetoday

maketitle
sectionINTRODUCTION
The aim of this study is to observe the dependence of the electrical resistance of two metals, Copper and Nickel, and of a doped semiconductor, the Germanium, as a function of the temperature. Furthermore our measurements allowed us to estimate the energy gap of the Germanium.
 %The two metals showed a linear dependence while the semiconductor has two different behaviour. Through our measuments 
 \

 The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... % <====================

blindtext % <==========================================================

blindtext

Blinddocument 

enddocument

The result is (see red arrows for the culprit):

The big white space results because LaTeX tries to fill the complete left column, because your class uses flushbottom, that means the last line of the column has to be at the bottom of the column. You can use raggedbottom instead to force not balanced colums.

MWE:

documentclass[twocolumn,prl,nobalancelastpage,aps,10pt] revtex4-1
 %documentclass[rmp,preprint]revtex4-1
usepackage[latin9]inputenc
usepackage[english]babel
usepackagetimes % <======================================== outdated!

usepackageblindtext % <============================ to add dummy text

raggedbottom % <=======================================================


begindocument

titleElectrical resistance of Cu, Ni and Ge in the range $120K$ - $400K$

author...

affiliation...

beginabstract 
We observed the temperature dependence of the electrical resistance of Cu, Ni and Ge in the range between $200K$ and $400K$. It resulted to be linear in the whole range for Cu and Ni. The one of the Ge exhibited this linear behaviour only up to $300K$ showing an exponential decay above. We also estimated the energy gap $E_g$ of Ge which resulted to be equal to $E_g=$
endabstract

datetoday

maketitle
sectionINTRODUCTION
The aim of this study is to observe the dependence of the electrical resistance of two metals, Copper and Nickel, and of a doped semiconductor, the Germanium, as a function of the temperature. Furthermore our measurements allowed us to estimate the energy gap of the Germanium.
 %The two metals showed a linear dependence while the semiconductor has two different behaviour. Through our measuments 
 \

 The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... % <====================

blindtext % <==========================================================

blindtext

Blinddocument 

enddocument

Result:

Now the white space is at the bottom of the column.

If you do not like that you need to rephrase your text in first column to fit.

If you delete for example one sentence The starting point of our discussion are ... with commented raggedbottom you have the following code

documentclass[twocolumn,prl,nobalancelastpage,aps,10pt] revtex4-1
 %documentclass[rmp,preprint]revtex4-1
usepackage[latin9]inputenc
usepackage[english]babel
usepackagetimes % <======================================== outdated!

usepackageblindtext % <============================ to add dummy text

%raggedbottom % <=======================================================


begindocument

titleElectrical resistance of Cu, Ni and Ge in the range $120K$ - $400K$

author...

affiliation...

beginabstract 
We observed the temperature dependence of the electrical resistance of Cu, Ni and Ge in the range between $200K$ and $400K$. It resulted to be linear in the whole range for Cu and Ni. The one of the Ge exhibited this linear behaviour only up to $300K$ showing an exponential decay above. We also estimated the energy gap $E_g$ of Ge which resulted to be equal to $E_g=$
endabstract

datetoday

maketitle
sectionINTRODUCTION
The aim of this study is to observe the dependence of the electrical resistance of two metals, Copper and Nickel, and of a doped semiconductor, the Germanium, as a function of the temperature. Furthermore our measurements allowed us to estimate the energy gap of the Germanium.
 %The two metals showed a linear dependence while the semiconductor has two different behaviour. Through our measuments 
 \

 The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... The starting point of our discussion are ... % <====================

blindtext % <==========================================================

blindtext

Blinddocument 

enddocument

and the result:

Sometimes rephrasing is better than everything else ...

it is to wide for comment: i cant reproduce your problem. with your code, which i slightly change preamble (changes had not influence to xour problem) i obtain the following result:

i test with recent version of MikTeX. so, see, if your LaTeX installation is up-to-date.

off-topics: i suggest to use ˙mchempackage for writing chemical elements and formulas, andsiunitx` for all values with units. see how is used in MWE below:

documentclass[twocolumn,prl,nobalancelastpage,aps]revtex4-1
usepackagetimes

usepackage[version=4]mhchem
usepackagesiunitx
usepackagelipsum

begindocument

titleElectrical resistance of Cu, Ni and Ge in the range 120,K to 400,K
author...

affiliation...

beginabstract
We observed the temperature dependence of the electrical resistance of ceCu, ceNi and ceGe in the range between SIrange200400kelvin. It resulted to be linear in the whole range for ceCu and ceNi. The one of the Ge exhibited this linear behaviour only up to $300K$ showing an exponential decay above. We also estimated the energy gap $E_g$ of Ge which resulted to be equal to $E_g=?$.
endabstract

datetoday

maketitle
sectionINTRODUCTION
The aim of this study is to observe the dependence of the electrical resistance of two metals, Copper and Nickel, and of a doped semiconductor, the Germanium, as a function of the temperature. Furthermore our measurements allowed us to estimate the energy gap of the Germanium.


lipsum[1-3]

sectionThe second section
lipsum[4-5]
enddocument